Spacewalking astronauts from the shuttle Discovery probably will try to revive a dead Navy communications satellite this summer -- possibly by "jump-starting" it in what would be the most daring and ambitious shuttle mission to date.

The crew of the 20th shuttle mission is expected to rendezvous in mid-August with a satellite put in orbit by a crew last month but now drifting uselessly.

The satellite's power supply failed to come on to deploy its antenna and fire its onboard engine to carry it to a permanent position 22,300 miles above the Equator. Efforts to revive it by flipping a switch with a "fly-swatter" extension on the shuttle's robot arm were unsuccessful.

"We're getting ready right now to do whatever the owner of that satellite wants . . . as long as we're convinced it's safe," Johnson Space Center director Gerald D. Griffin said in an interview. The possibilities include retrieving the dead satellite and returning it to Earth or "jump-starting" it to get its engine to fire on commands from the ground. Either way, two astronauts would have to walk in space.

One reason such a rescue mission would be daring is that the satellite is loaded with hydrazine, one of the most flammable and toxic fuels used in space. Another is that the Minuteman solid-rocket motor aboard the satellite never fired last month and could ignite.

"The likelihood of that happening is very, very remote," Griffin said. He said the likeliest option is to have astronauts unscrew a panel on the satellite and attach cables to electrical connections that bypass the satellite's timing and arming device, putting the satellite under direct control of the ground.

After the astronauts returned to Discovery and the ship moved off to a safe distance, flight directors working for the satellite's owner, Hughes Communications Corp., could instruct the satellite to go through its sequence of commands, ending with engine firing to lift the satellite to a "geostationary" orbit where it would serve as a radio relay for the U.S. Navy.