NASA engineers managed to restore steady contact with the elusive Magellan spacecraft orbiting Venus yesterday after it put them through a grueling game of hide-and-seek that lasted 21 1/2 hours.

Success came at 7:33 p.m. EDT and "took a ton off our shoulders," said Tommy Thompson, Magellan science manager. "We're going home with smiles on our faces."

A National Aeronautics and Space Administration tracking station first detected a signal from Magellan, the first since Tuesday night, at 3:30 p.m. EDT yesterday, just after the craft emerged from behind Venus, officials said. After several maneuvers, engineers managed to make the contact steady four hours later.

In the manned part of the space program, officials reported yesterday that they have literally "flushed out" the culprit most likely responsible for at least part of a hydrogen leak that halted the launch of the space shuttle Columbia earlier this summer: tiny glass beads, half as thick as a sheet of paper, that may have contaminated the system at the factory where the leaky parts were made.

The beads emerged when engineers flushed fluid out of the leaky fuel system after it was removed from the shuttle, said Bill Lenoir, who heads the manned space flight office.

Still, tests have failed to recreate the same amount of leakage that occurred on the pad.

"We couldn't conclude conclusively what the source of the leak was," Lenoir said. The leaky parts have been replaced on Columbia for the astronomy mission, now set for launch Sept. 1.

Engineers will conduct further tests on an equally elusive leak that prevented the launch of the shuttle Atlantis on a secret Department of Defense mission in June, he said, adding that initial tests of fuel system components will be "more rigorous."

In a progress report on the proposed space station Freedom, project director Dick Kohrs said engineers have made "tremendous progress" in reducing weight and power problems in the design. The projected weight is now within 35,000 pounds of the goal, instead of 143,500 pounds over it as in the design earlier this year, he said, and the power is within one kilowatt of the requirement.

These changes have also helped reduce maintenance requirements for the station, which were found by a NASA team to be far over what the station's astronaut crew and robots could handle. Engineers are continuing to work on that problem, he said.

Since it was learned in June that the $1.5 billion Hubble Space Telescope was launched with a built-in flaw in its main mirror, NASA has been under pressure to prove it can manage big space projects. The hydrogen leaks that prompted shuttle officials to ground the manned fleet at about the same time as the announcement of the Hubble flaw intensified the criticism.

Officials had looked to Magellan to break the flow of gloomy news, and they were elated to get the Venus probe back on track.

By mid-day, the spacecraft had failed to respond to repeated computer commands beamed across 149 million miles of space toward its orbit around Venus. "Bad news. Nothing. Not a peep out of it," said spokesman Bob MacMillin at the Jet Propulsion Laboratory in Pasadena, Calif., which manages the mission for NASA.

Contact was lost at 10:03 p.m. EDT Tuesday, just hours after Magellan officials had released the spacecraft's first images of Venus. The craft was already in a "safe mode," with some systems shut down, as engineers tried to figure out what had caused it to lose contact the first time last Thursday.

Data coming in at the time the signal was lost Tuesday night indicated the spacecraft suddenly rotated itself and its transmission antenna away from Earth at a rate of about one-half degree per second, apparently because the onboard computer "thought it needed to do something," Magellan scientist Steve Wall said.

The "good news" is that the manner in which the signal was interrupted indicates "there was no massive failure on board," Wall said. "We at JPL are very hopeful we'll be able to do something" to fix the craft.

At about 3:30 a.m. EDT Wednesday morning, engineers decided to send a command to Magellan "in the blind" -- that is, with no signal coming from the craft -- "to avoid any risk that the spacecraft batteries might run down," program engineer David J. Okerson said.

They did this to remind Magellan not to swing its solar panels out of the sunlight required to supply the craft with electrical power, he said.

If the solar panels are not receiving enough sunlight, the craft may switch to its limited battery power, he said.

When the vehicle failed to respond, he said, "We scratched our heads a while." The craft also failed to respond to a second set of commands sent at 9:45 a.m. EDT yesterday.

Then the engineers decided to send a more complex set of commands designed to set Magellan sweeping the sky with its radio signals in hopes they would hit Earth. That led to the first blip of contact and eventually enabled engineers to lock onto the craft.

Okerson said Magellan "has proven itself to be extremely robust -- as it were, able to take care of itself."

The spacecraft, launched from Kennedy Space Center aboard a space shuttle in May 1989, was the first U.S. planetary mission since 1978, and the first Jet Propulsion Laboratory planetary flight since the Voyager probes in 1977.

Scientists had breathed a sigh of relief when Magellan went into the desired orbit around Venus on Aug. 10.

It was supposed to begin a 243-day mission to map the surface of the cloud-covered planet using advanced radar on Sept. 1.