According to now-declassified documents, the US had the capability but chose not to launch a satellite due to setting legal precedent. I.e., they wanted to launch spy satellites but were worried that if they initiated this, it could be interpreted as an act of war. If instead the USSR was first to launch a satellite and it flew over the US, then the US could do the same in turn without provoking war.

See, e.g. http://www.pbs.org/wgbh/nova/military/sputnik-declassified.h...

Here is some of the transcript from that:

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> NARRATOR: What Eisenhower most wants is information about the enemy's forces. Early in 1954, he authorizes illegal military over-flights to photograph the Soviet Union.

> R. CARGILL HALL: This was a major presidential decision. These peacetime over-flights of the Soviet Union were very risky, first of all because these aircraft could not operate at altitudes above Soviet air defenses.

> NARRATOR: March, 1954: American fighters photograph Soviet air bases near Vladivostok. In April, American planes again enter Soviet airspace. But in May, Eisenhower's strategy backfires. An American bomber flies into Russia and is attacked by Soviet fighters. The damaged bomber barely makes it home.

> It is 1954, three years before Sputnik. Eisenhower is committed to surveillance of the Soviet Union. But he needs a better way.

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> By early 1955, Eisenhower is set on creating a reconnaissance satellite. But the Killian Report has pointed out a problem: the legal status of space has not been defined.

> National boundaries extend into the atmosphere, but how far up does territorial airspace go? The answer will be critical to Eisenhower's spy satellite plan.

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> LEE WEBSTER: When we fired that, we knew we could put a vehicle in orbit, because we had the velocity that it required. If we'd been given the go-ahead, we could have beat Sputnik by a year. We had the hardware over in Redstone, sitting in warehouses ready to go.

> RANDY CLINTON: We could have beat them. And that's the thing that grabbed us, hurt the most, is we knew, ahead of time, that we could have beat them.

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> Just a few days after Sputnik was launched, Donald Quarles, from the Department of Defense, is in the Oval Office talking to Eisenhower. And one of the points that he makes is that he thinks that the Soviets have done us a good turn. They had established a precedent of over-flight, exactly what Eisenhower wanted to do initially, and now the Soviets had done it for us.

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I'm not sure this is the complete story (I realize the above may come off as blindly pro-US), but it's an element that was unknown for 50 years while that information was still classified. I think the access to scientific papers is not a key part of that event (and besides, 50 years ago the traditional scientific publishing model still made sense).