This is almost definitely "Noise Level" (1952) by Raymond F. Jones.

The only difference is that instead of telling the scientists that the Soviets had developed working anti-gravity, the project leader showed the assembled scientists a (faked) movie showing the anti-gravity device in operation, and claimed that the government had lost his notes.

The scientists do ultimately succeed in developing anti-gravity, though they initially think their efforts are a failure because their machine is much bulkier and uses a lot more power than the one they were shown.

The story was originally published in Astounding, but it's been anthologized a few times. If you read it in an anthology, it was most likely Spectrum V (also Spectrum 5 depending on the edition).

This is almost definitely "Noise Level" (1952) by Raymond F. Jones.

The only difference is that instead of telling the scientists that the Soviets had developed working anti-gravity, the project leader showed the assembled scientists a (faked) movie showing the anti-gravity device in operation, and claimed that the government had lost his notes.

The scientists do ultimately succeed in developing anti-gravity, though they initially think their efforts are a failure because their machine is much bulkier and uses a lot more power than the one they were shown.

The story was originally published in Astounding, but it's been anthologized a few times. If you read it in an anthology, it was most likely Spectrum V (also Spectrum 5 depending on the edition).

This is almost definitely "Noise Level" (1952) by Raymond F. Jones.

The only difference is that instead of telling the scientists that the Soviets had developed working anti-gravity, the project leader showed the assembled scientists a (faked) movie showing the anti-gravity device in operation, and claimed that the government had lost his notes.

The scientists do ultimately succeed in developing anti-gravity, though they initially think their efforts are a failure because their machine is much bulkier and uses a lot more power than the one they were shown.

This is almost definitely "Noise Level" (1952) by Raymond F. Jones.

The only difference is that instead of telling the scientists that the Soviets had developed working anti-gravity, the project leader showed the assembled scientists a (faked) movie showing the anti-gravity device in operation, and claimed that the government had lost his notes.

The scientists do ultimately succeed in developing anti-gravity, though they initially think their efforts are a failure because their machine is much bulkier and uses a lot more power than the one they were shown.

The story was originally published in Astounding, but it's been anthologized a few times. If you read it in an anthology, it was most likely Spectrum V (also Spectrum 5 depending on the edition).