The space agency has abandoned attempts to revive its $95 million Seasat satellite, which mysteriously went silent over the Atlantic Ocean 99 days after it had been put in orbit.

"The bird has expired, no question about it," Alan M. Lovelance, deputy administrator of the National Aeronautics and Space Administration, said yesterday in an interview. "We've tried any number of times to get signals into the bird and get them out, without any luck at all. We're now convinced the patient is lost.

The first satellite built to observe the world's oceans, Seasat suffered on Oct. 10 what space analysts think was a massive short circuit that turned off its power supply and rendered it unable to transmit or receive any signals.

A Seasat Accident Review Board has still not pinpointed the cause of failure but has ruled out any chance that it was interfered with from Earth or from orbit by another satellite. Several published reports suggested that a Soviet "hunter-killer" satellite had rendered tha U.S. spacecraft useless.

"That's nonsense," a NASA official said. "There was no Soviet satellite anywhere near it when Seaset went silent, which was somewhere over the Atlantic north of the equator as it moved south from Great Britain toward the next ground station in Santiago, Chile."

Whatever the reason the failure was costly. The $95 million satellite was one of a kind, built to orbit 90 percent of the world's oceans from an altitude of 500 miles. Its five instruments were to watch icebergs and track ships to follow stroms as well as tides and currents, and to record ocean surface temperatures to within one degree.

Seasat's 99 days were fruitful, according to NASA officials, who said the satellite's unique onboard radar gave scientists 60 hours of information about the movement of ships and ice floes around the entire world.

"What we'll miss is the infromation it would have supplied on the ice sea in the coming winter months," one official said."There's no way we can diplicate what this satellite would have both hemispheres."

The satellite also missed observing the change in sea conditions from season to season. Put into orbit in June the satellite had just begun to observe autumnal changes when it failed. I had no chance to watch for winter changes.