The trouble-ridden and oft-postponed 16th flight of the space shuttle got a green light today after an 11th-hour repair job fixed a leaking experiment and saved one of seven crew members from getting bumped.

Weather permitting, a crew of five astronauts, an engineer and Sen. Jake Garn (R-Utah) will roar away from Earth on the spaceliner Discovery at 8:04 a.m. EST Friday on a five-day mission.

"The cargo is intact and the crew is intact," NASA Associate Administrator Jesse W. Moore said this afternoon at a news conference delayed two hours by salt water from an experiment leaking into the shuttle's mid-deck.

"We have corrected the leak and contained it," Moore said. "The experiment will fly, Charlie Walker will fly and we're ready to fly."

Walker, an engineer with McDonnell Douglas Corp., has as his sole space project an experiment to produce an unidentified hormone that can't be manufactured on Earth. Walker was about to be bumped when technicians boarded Discovery and stemmed the leak with several quick turns of a wrench.

By early tonight, the only thing threatening Discovery's mission was the weather. A low-pressure front carrying rain and thunderstorms from the Gulf of Mexico was on a course that could bring it over central Florida at launch time. But forecasters said a high-pressure ridge moving down from Cape Hatteras could block the front and bring in weather suitable for liftoff.

"It's a 50-50 proposition right now," Air Force Capt. Art Thomas said.

There are two launch "windows," or suitable periods, on Friday morning for the fourth flight of Discovery and 16th mission of the shuttle program. The first "window" opens at 8:04 and closes at 8:18. The second opens at 8:45 and shuts at 9 a.m.

If both windows are missed, the flight is to be rescheduled for Saturday.

The mission is to end back at Florida's Kennedy Space Center at 8:15 a.m. Wednesday.

Besides Walker and Garn, the crew includes commander Karol J. Bobko, pilot Donald E. Williams and mission specialists Margaret Rhea Seddon, Jeffrey A. Hoffman and S. David Griggs.

The mission being flown Friday was scheduled originally for Feb. 20, then postponed to Feb. 27 and delayed again twice in March before being rescheduled for April 12. Crew members were switched four times and spacecraft twice.

The postponements and substitutions also involved the combining of two flights and two sets of payloads. A plan to deploy a $100 million communications satellite was removed from the manifest in February and a plan to retrieve a satellite from orbit was scrubbed to allow room in the cargo bay for the combined payloads from two flights.

"The launch team is really looking forward to this one," launch operations director Robert Sieck said. "We've had a long dry spell here since January and we'd like to get things going again."

On its first day in orbit, the crew is to deploy a Telesat communications satellite for Canada and begin conducting the hormone experiment that stirred so much trouble today. On the second day in space, the crew is to unload a Leasat communications satellite for the Navy, the third of its type to be deployed in orbit by shuttle crews in the last nine months.

The remainder of the mission is devoted to medical experiments and a novel test of how mechanical toys behave in space.

The toys include a small mechanical mouse (nicknamed The Rat Stuff), a magnetized wheel, a paddle and ball, a windup car, a set of magnetic marbles, a ball and some jacks, a helical spring, a top, a gyroscope and a yo-yo. Each astronaut is responsible for a different set of toys.

"This experiment is not a joke," Bobko said recently. "It is a serious experiment that will be filmed in space and shown to elementary and high school students as a serious way to get them interested in science."

Garn's main task will be to measure his body's responses to weightlessness and record his responses if he should feel ill in orbit. Said Garn at his only news conference before the mission: "Nobody will remember a year from now whether I measured my blood pressure or got sick or how these toys behave in orbit. They'll remember whether the crew got those satellites out into space or not."