Two astronauts walked in space a record length of time today in an extraordinary attempt, scheduled to continue Sunday, to revive a Navy satellite that has been in orbit but inoperable since April.

James D. van Hoften, 41, and William F. Fisher, 39, spent seven hours and eight minutes in the open cargo bay of the space shuttle Discovery, where they fastened Discovery's mechanical arm onto the 15,000-pound Leasat 3 satellite to begin the salvage attempt.

After Fisher exposed the satellite's electronic connections, he said he could see no evidence of what caused the satellite to go dead when it was deployed into orbit by a previous shuttle crew. "There is no evidence of debris on anything that would cause a problem. It's clean as a whistle," he said.

Van Hoften and Fisher retrieved the drum-shaped satellite from orbit, bypassed the timing lever that had failed to put the satellite into operation in April and then disarmed the satellite's Minuteman rocket motor, which could have ignited as the astronauts worked on the satellite.

The astronauts plugged portable battery packs into the satellite's lifeless electrical system, feeding it power for the first time since its April 13 deployment.

The astronauts were able to move the satellite's two 12-foot-long antennae, showing flight directors at Houston's Mission Control Center that they had started at least part of the satellite.

"How's that for lookin' good," Fisher called out. "Hot dog! Look at that, Jack."

Van Hoften and Fisher were outside the shuttle from about 8:00 a.m. to shortly after 3:00 p.m. EDT, breaking by one minute the spacewalk record set by van Hoften and George D. Nelson in April 1984, when they repaired a scientific satellite, Solar Max.

"It's not over yet, and we have another tough day ahead of us tomorrow. But we had a perfect rendezvous this morning and a very successful spacewalk," Flight Director William Reeves said this evening at the Johnson Space Center in Houston.

"It's still a 50-50 chance that the satellite will be salvaged successfully," Reeves said. "The encouraging thing is that the satellite accepted power. Every indication is that the repair did exactly what it was supposed to do today."

Although the two crewmen accomplished more than half of what they set out to do on the salvage mission, they are planning a four hour spacewalk to start at 7:40 a.m. EDT Sunday to finish the job.

On Sunday, the astronauts are scheduled to place a "space blanket" over the engine bell that serves as the rocket nozzle for the satellite's Minuteman motor to use the sun's heat to warm it. Leasat has been in the deep cold of space so long that its rocket motor is expected to be too cold to be fired correctly.

Their last task on Sunday is to install a vertical bar along the 20-foot length of the satellite to serve as a handle for van Hoften to spin the satellite and push it away from Discovery into space. If it starts spinning, it will spin indefinitely, giving it stability in orbit.

When the astronauts release the satellite from Discovery's cargo bay, Leasat's future is in the hands of fate. It will be seven days before enough power can be fed into the satellite to thaw its liquid fuel tanks and almost two months before the solid-fueled rocket motor is warm enough to be ignited by commands from Earth-bound controllers.

The record-setting spacewalk was not without difficult moments. Van Hoften and Fisher had to deal with a robot arm whose backup motor was crippled, forcing astronaut John M. Lounge to move it slowly from inside the shuttle cockpit.

Van Hoften accidentally dropped or kicked a trash bag he was using to store tools as well as screws and plates removed from the satellite. "There's a hole in the trash bag," van Hoften said in exasperation. "I can't believe the whole thing opened up on me and we lost at least one screw.