"Earlier" covers a lot of ground. Danwild6's thread is "just a little bit earlier--unleash von Braun!" But OP specifies (or very strongly suggests anyway) a whole decade or more earlier.
Back at you, Truth Is Life--you and the other guys I think of as the high-tech gang around here are just the people I'd have gone to to
ask "How early could anyone have possibly have orbited anything, given that the general trajectory of technical development was as OTL?"
Unless we assume PODs involving earlier leaps forward in technical ability--and I believe making a rocket work better earlier would involve many small increments of capability across many separate fields, not one single burst of inspiration in one field, so we'd be talking about ASB rolling successive sevens in that case--it becomes a matter of "how much crude but big rocket can enough money buy in timeframe X" and "how high can a budget/national commitment (at some point, effort transcends mere dollar cost and enters the realm of conscious sacrifice) go in said timeframe X?"
So--if Harry Truman were convinced that the USA had to get a functional satellite into orbit as soon as possible--presumably in the late 1940s everyone would be agreeing to accomplish anything there beyond merely pointing at an orbiting grapefruit and bragging "I did that!" such a craft would have to be manned--and he had the evidence to add to his normal political arm-twisting skills to convince as many key players as he needed to to back his crash program--what sort of design, attainable with known 1948 technology with money no object, could put something massing say 5 metric tonnes into LEO? (And also accomplish prior research in things like reentry systems allowing any astronaut sent up to hope to survive!) Is it just a matter of throwing enough money at it and scraping together something attainable that just costs a lot, or is it a matter of having to learn how to do things men like von Braun or Korolev could conceptually imagine but not know, yet, in any detail, just exactly how to practically do?
Like, could one orbit (say we count a beeping grapefruit as meeting the specs of OP, presumably the real, manned satellite follows later) a minimal satellite with A-4 (aka 'V-2') type alcohol/oxygen engines? Could off-the-shelf improved A-4 type engines simply be clustered together by the dozens or hundreds to achieve sufficient thrust, and could this thrust be sufficient to boost really huge tanks of alcohol and LOX (huge to make up for the poorer ISP of alcohol/LOX)? All this just to get some test object into orbit to prove it can be done, and maybe do some very elementary research into the space environment, just to pave the way for future launches of manned capsules.
Can it be done in 1948? Well, surely not in just one year! But putting the questions that way makes me want to answer--yes, spend enough money and just go with stuff available already, just purchased in truckload lots, and someone like von Braun ought to be able to get something into orbit, given extravagant wastefulness.
Then I want to recoil and ask why, if it could have been done, it wasn't. Surely if he could do that, given enough money, von Braun could also have delivered a crude but working ICBM a decade or so before anyone had one; if he or some American "beard" could go before the appropriate Congressional committees with a set of blueprints using off-the-shelf stuff to quickly develop the
capability to lob bombs onto the Russians during say the Korean War, surely they'd just go ahead and write the check?
And then, it would be a very simple matter for him to say to the committee, "By the way, this same rocket can put 70 percent of the mass of the warload we've designed it for into Earth orbit; if we do that and say it is all for science, the Soviets will see for themselves we can also bomb them and we never have to make the threat openly."
I imagine that would be warmly appreciated by the committee. And this is pretty much how it went between Korolev and Khrushchev OTL.
So now I'm back to doubting it could have been done for any amount of money, not without technical breakthroughs allowing key bottlenecks to be bypassed.
For instance, it sounds very well to just cluster together lots and lots of V-2 type engines. But if a single failure of one of the units of the cluster leads to failure of the whole rocket, then each unit we add multiplies the chances that the rocket won't work, or worse, blow up spectacularly (and probably doing lots of property damage, and maybe killing a lot of people). It could be that by the time you've bolted together that many mini-rocket units, you've got yourself a near-surefire bomb sitting on the pad.
Or, the mission of the A-4 rocket was to lift a decent-sized load a rather short distance at a sadly inadequate velocity to achieve orbit. To get to orbit using that kind of engine, one would have to push a far lighter load (per rocket unit, far heavier overall!) for a much longer period of time--could be that the known designs just wouldn't last long enough to deliver the necessary delta-V, they'd burn up first or something like that.
One might try using a whole lot of stages, each stage having rockets that burn about as long as current design allows, then starting over with fresh rockets.
But this and clustering in general both highlight the key variable, engine mass versus delivered thrust--if a sufficiently reliable engine set winds up weighing too much at a given state of the art, it can't do the job at all no matter how much money you throw at it. To what extent were the limits on rocket engines in 1948 a matter of insufficiently developed design, and to what extent a matter of insufficiently capable materials (and associated know-how of how to machine them?) To what extent could these two limits be pushed ahead by simply raising the scale of the budgets, hence size of the development teams? To what extent then, was the timescale of development of rockets that could do the job a matter of neither Americans nor Russians having the political will to put a lot of money (or Plan priority) down on a risky, unproven venture of unclear utility, and to what extent was it a matter of simply having to wait for the general state of the art to advance to necessary levels?
What about related technologies that also needed to be developed and integrated into the design? What about avionics for instance--how "smart" does a rocket capable of delivering something to orbit have to be, and it this was a constraint, how long would it take, given lavish funding, to get a package that was robust, reliable, and light enough to do the job? What about tankage--could the 1948 state of the art deliver sufficiently light and reliable tanks for liquid oxygen in the sorts of quantities needed, light and yet strong enough so that, perhaps at some crude sacrifice, they'd hold well enough? Or did that too have to wait OTL for years of patient trial and error and gradual improvements being serendipitously developed by industry as a whole? Could those developments also be accelerated by pumping in enough money?
Could it be done with alcohol/oxygen at all? Should it instead have been done with "storable" hypergolics or the like as on the Titan missile or many Soviet ones, and if so were the alternative engines available or if not how fast could they be forced online? Or must the program wait on developing kerosene/LOX engines?
These are technical questions! If I wanted them answered here on AH, you, Truth of Life, are among the first people I'd PM for an answer! I'd also ask e of pi and Asnys.
Here's my best guess: no way no how could any amount of money get a satellite up with anything on the shelf in 1948. If it could, I'd think the USA would have had some crude, massive, inefficient, vulnerable, expensive--but effective--ICBMs sitting on launch pads ready to launch (in about half a day, after getting the go code, since they'd need to be fueled up) before 1955. Well before 1955 in fact. Even given the high mass of the early A-bombs and H-bombs, I'd think that if near-orbital speeds were in the cards by 1950 and it was just a matter of scale, they'd get funded on sufficient scale.
So the satellite is not going up in 1949; it isn't just a matter of cobbling a crude but effective booster together. A certain amount of research and development must intervene, and only then can the minimal rocket be designed and built.
What I do not know is, how much can the rate of development be speeded up by simply spending more money.
Suppose an ASB bird whispered in President Truman's ear, just how much money was spent OTL between 1948 and 1957 on all the various rocket development projects put together, adjusted to 1948 dollars. What would that lump sum be? Would it be of a scale that the President could possibly demand as vital for next year's budget? Would that amount of money, whatever it is, presumably capable of buying all the man-hours spent OTL over a 9 year period on all the American rocket programs, be sufficient to fund all necessary preliminary work, then actual experiments, then in the light of their results the necessary advances and solid designs, within a year? Or two? I'm guessing not. You'd need several years of such crash funding.
What would that dollar amount be? How would it compare to say the entire Department of Defense budget? (Much smaller, I'd guess; the rocket programs OTL were just one set of many many plates our MIC had spinning that decade). Suppose Truman could get a budget equivalent to say, the entire budget of the Air Force for a year added to the Federal kitty, and spent all that extra money on the rocket program--would that buy a working blueprint for fiscal 1950 to build and launch? I'm guessing maybe and maybe not, it depends on whether the OTL successes depended on advances in state of the art that just had to wait to happen naturally, or not.
With one thing and another, I'm guessing that at the very earliest, given a national crash priority accepted as necessary way back in the late 1940s (but why?) perhaps the first orbit could be achieved five years earlier, in 1952.
Back to you on that Truth, what do
you think?
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As for just barely getting the jump on Korolev by unleashing von Braun--I think "anon-user" captured the nature of Eisenhower's priorities better than danwild6's thread did several years ago. Ike wanted America in space, he wanted us there first, but his reasons for prioritizing a nominally civilian (though run by the Navy!

) project Vanguard were a matter of setting a precedent, precisely because his real focus on space was to get satellite intelligence--that was the secret Lockheed project, Corona, commissioned by the CIA. He wanted Vanguard to get that beeping ball up pronto because once it had orbited, the Russians would be in a weaker position to protest spy stuff.
Therefore von Braun's team was kept on ice, because he (and much of his team!) not only had their Nazi V-2 past, but had subsequently spent the past decade plus working for the Army, developing weapons systems aimed straight at the Soviet Union's forces.
Now, if Ike had had that little ASB bird chirping in his ear, perhaps he could have doubled down on his plan by making Vanguard a completely civil project, creating NASA or something like it earlier, and funding it much more lavishly than OTL and giving much more of a priority, to guarantee both that the first satellite to orbit be American, and that it be beyond all doubt a civilian, peaceful, scientific accomplishment.
But actually, he might do something else instead--while keeping Corona funds coming, maybe
back off Vanguard, reasoning that it's really at the end of the day just a dummy program, and what he really needs is for, as OTL, the
Soviets to orbit that first satellite. If their right to protest future satellites might be muddied up a bit if they chose not to protest Vanguard (and after all, they just might choose to protest it!), how much stronger a precedent is it if the first object in orbit is their own, and they didn't bother to ask anyone else's permission first? After Sputnik, Corona launches were golden, just another satellite which the Soviets themselves had implied moved in free, international space where any object has a legal right to be as long as it isn't actually shooting at anything.
Eisenhower probably wouldn't even cut back Vanguard, because the fact of the American program progressing (however fitfully and unimpressively) had some bearing on Khrushchev's decision too; had there been no American program whatsoever, he might not have felt the stakes were high enough to take the gamble.
Doing exactly as OTL gave Ike almost everything he really wanted; he might have preferred to have America look less silly and backward, but he knew the real "correlation of forces" as his Soviet counterparts would put it, and nothing could clear the way for Corona better than a Soviet first in orbit. So embarrassment and even possible political losses for his party (which remember, he was recruited to and not a rabid ideologue of) might have seemed to him, in retrospect, small prices to pay for what was really vital to US national security.
Once that overriding purpose was accomplished, Ike did indeed unleash the von Braun team and America's first satellite to orbit was a fine piece of work, one that immediately began to advance science.
Could this have been true of some crash-priority, Manhattan-Project or even greater scaled race to launch half a decade or so before? Probably not.
I think it is safe to say, to get a significantly earlier satellite launch, one would need a POD where one or both of the leaders of the major power blocs had some overriding need to get something in orbit ASAP, and without going into ASB territory it is hard to imagine what that priority would be. Missiles were already a high priority for both sides, and something capable and reliable enough to lob the sort of big bombs they had in the mid-50s truly intercontinental distances could surely orbit at least something as minimal as Sputnik-1 or Vanguard. Once they had the ICBMs it was only a matter of time before one side or the other would launch an orbiter of some kind, in part because both sides realized the utility of satellite surveillance. Yet, with both missiles and spy satellites on the agenda from very early in the decade, both powers proceeded at the pace they did and no faster. I suspect that accelerating that pace much would have required disproportionate funding--to double the pace you'd need more than to double the annual budget, and would wind up spending more money than OTL per given result. Probably, the faster you try to force it, a lot more. To explain why either state would choose to do so you'd need motives much more urgent and prioritized than were evident OTL.