Cannibalizing parts from their spacecraft, the shuttle's astronauts today fashioned a makeshift extension for Discovery's robot arm and prepared to use it to try to revive a Navy communications satellite dead in space since it was deployed from the shuttle's cargo bay Saturday.

The way things stood tonight, two crew members are to spacewalk into the cargo bay Tuesday and attach three jury-rigged devices to the end of Discovery's 50-foot mechanical arm. On Wednesday, after the shuttle nudges close to the satellite, another crew member is to manipulate the arm and its extension in hopes of freeing an arming lever on the satellite.

If the delicate maneuver succeeds, the satellite could come back to life almost immediately. Then, according to the plan, 40 minutes later -- with Discovery safely in the distance -- the satellite's engines would ignite to send it into proper orbit.

"This thing is beginning to look just like a lacrosse stick," Discovery pilot Donald E. Williams told the flight team at Houston's Johnson Space Center who spent the day instructing the crew how to rig the "Rube Goldberg" devices they'll use to try to rescue the $40 million satellite.

By 6 tonight, the interior of Discovery's cabin looked like a garage sale. Pilot Williams and commander Karol J. Bobko scavenged lengths of rubber hose from water kits, aluminum frames from window shades and plastic covers from flight plans.

Astronaut Margaret Rhea Seddon sewed the plastic covers together to form cones that will be attached to the extension arm and used to flip the arming lever.

Astronauts Jeffrey A. Hoffman and S. David Griggs were busily readying their spacesuits for Tuesday's unplanned and unrehearsed spacewalk.

Even Sen. Jake Garn (R-Utah) got in the act, backing up against one of the windows to serve as a shade to keep the sun out of Seddon's eyes as she sewed.

"This has been some flight," pilot Williams said late today. "First, we had toys in space, and now we have arts and crafts."

"We advance to watercolors tomorrow," astronaut Jerry Ross replied from the Johnson Space Center.

Flight directors were far from certain the maneuver would succeed, but there was little else the crew could do.

"We're doing the best with what we've got right now," flight director John Cox said. "There are a lot of folks trying to make something good out of a situation that went to pot three days ago."

What went to pot was the Navy's Leasat satellite, the second of two satellites deployed out of Discovery's cargo bay and the third of three Leasats the Navy wanted in orbit to provide radio links between ships at sea and bases on shore.

A lever intended to spring out from the satellite and trip a clock inside the satellite apparently did not budge. The clock never started, the satellite's antennas never snapped into place, the drum-shaped satellite never began to spin to orient itself and its Minuteman engine never fired to carry it to "geostationary" orbit 22,300 miles above the Equator. Tonight the satellite was orbiting uselessly about 50 miles ahead of Discovery.

The plan hatched by flight directors tonight is to have astronauts Hoffman and Griggs go into the cargo bay on Tuesday to attach three extensions to the robot arm. Two look like fly swatters and the third like a lacrosse stick.

On Wednesday Bobko and Williams are to bring the DC-9 sized shuttle alongside the satellite. From inside the cockpit, Seddon is to maneuver the robot arm and its extensions up against the spinning satellite in the hope of snaring the jammed arming lever like a child on a carousel tries to grab the brass ring. The three extensions are being put on the arm in case one or another fails.

There's no guarantee the crew will be able to rendezvous with Leasat, much less salvage it. Discovery's crew did not train for a rendezvous and did not have the rendezvous maneuver programmed into its navigating computer, an oversight it was to correct tonight by reprogramming the computer with instructions from the ground.

If Seddon can snare the satellite's lever and start its clock, there is a good chance the satellite can be saved. Once the clock starts, the antennas are supposed to deploy, the satellite to speed up its spin and the engine to fire. The sequence takes about 45 minutes.

If the clock is started, crew safety becomes the overriding consideration. Bobko and Williams would have to fly Discovery at least 12 miles away from the satellite and raise the shuttle's nose so that the cockpit windows don't face the satellite's engine. Even at that distance, the rocket exhaust from the satellite could fog the windows so badly the crew would not be able to see out.

Earlier today, crew members frolicked with mechanical toys they had brought along to photograph as a demonstration of physics in space for elementary and junior high school students.

The seven crew members demonstrated in weightlessness how a top behaves, how a yo-yo works, how a Wheel-O gets started, how a set of magnetic marbles moves and how a mechanical mouse moves across the cabin.

"There are an infinite number of combinations and variations we can do with these," astronaut Williams said as he played with magnetic marbles and juggled balls by moving them from one position to another like pawns on a chess board. "Any smiles on our faces are just simulated, you realize," he said.

Seddon showed how to play with a ball and jacks in space, then how to work a "Slinky" in weightlessness. Said Seddon as she moved the spring-like Slinky from hand to hand: "It will slink from hand to hand, but it won't slink at all out of one hand. That's what toys are like in space."