Among the first victims of the Carter administration's new cuts of the federal budget were 70 graduate students whose grants were canceled last Saturday by the National Science Foundation, just before being mailed.

The NSF literally pulled 70 letters to fellowship winners out of its mail room as the congratulatory notices were about to go out. The 70 were awards of new grants; 390 letters renewing previous grants were allowed to go out.

The 70 winners, who suddenly became losers, may never know how close they came. The letters they were to get would have been their first news that they had won the awards.

While the NSF was silent publicly about its action, sources said the decision to trim some of the awards from 460 being granted was a direct result of the new budget squeeze.

"It's the feeling at the NSF that this is a fairly late decision," one source said. "The size of our budget cut has not yet been determined, but there's no question that some money will be cut."

The 70 losers would have won grants of $4,320 a year to pursue three years of full-time graduate study. This amount was up from the $3,900 awarded to graduate fellowship winners a year ago, and reflected inflation.

The NSF mailed letters to the 390 fellowship winners who had won awards last year or the year before and were still in line to receive NSF funds for another year.

"It's only the new starts that were cut," an NSF source said. "None of the old winners lost their award or was asked to even take less money."