A freak accident yesterday damaged the space shuttle Discovery and seriously injured a technician at the Kennedy Space Center, probably forcing another delay in the spaceliner's next flight, which had been scheduled about March 29.

It was the fifth flight postponement for Sen. Jake Garn (R-Utah), whose earlier planned trip aboard the shuttle Challenger was canceled because of problems with the satellite it was to launch. Garn is chairman of a subcommittee dealing with funding for the National Aeronautics and Space Administration.

The Florida accident occurred about 8 a.m. The bucket of a "cherry picker" crane hovering over Discovery fell, hitting a Lockheed technician on a work platform and then striking Discovery, which was horizontal on the floor of the Orbital Processing Facility being readied for movement into the Vehicle Assembly Building later in the day.

The falling 2,500-pound bucket struck Gary Sutherland, 35, breaking his left leg and injuring his shoulder, then fell onto the closed left-hand cargo bay door of Discovery. There was visible damage to the door, which is so thin and made of such lightweight material that it cannot be opened on Earth without elaborate supports to keep it in a fixed position.

The bucket left two holes about three feet apart in the heat protection tiles that insulate the door. Officials said the impact damaged several tiles and the door's structure.

"We have convened an investigating board to determine the cause of the accident, the extent of the damage and its impact on our flight schedule," Kennedy Center spokesman Mark Hess said. "Obviously, the schedule as it stands now has been moved back and the movement of Discovery to the launch pad on its scheduled date of March 14 is in jeopardy."

The 2,400-pound door probably will have to be replaced, which could involve shipment of a new door from the manufacturer and as many as three or four days of work to complete installation.

Nothing was in the cargo bay and no tanks or rockets had yet been mated to Discovery. The two satellites that Discovery is to carry into space are in a payload holding room at the launch pad waiting to be placed inside.

Discovery was due to fly no earlier than March 29 and probably a little later.

The upcoming flight is a combination of Discovery's next mission and a mission of the shuttle Challenger that was scrubbed when electrical failures in a $100 million communications satellite in its cargo bay were discovered five days before liftoff.

A cherry picker, on a traveling catwalk that stretches across a shuttle in a hangar, has two buckets, each big enough to carry two persons. The buckets, operating hydraulically on telescoping shafts, raise and lower workers so they can service satellites and other payloads in the shuttle's cargo bay.

NASA spokesmen said they had no idea why the cherry picker's bucket ripped loose. An investigative team was to meet last night and work through the weekend; investigators were called in from Houston's Johnson Space Center and the Rockwell International plant in Downey, Calif., where Discovery was designed.

The injured technician was described as hospitalized in "stable" condition last night.

The Associated Press quoted Sutherland in a telephone interview from his hospital room as saying: "I heard a bang and I looked up and saw the bucket coming down on me. I tried to duck but the bucket grazed my back and then hit my leg."

He said he crumpled onto the platform, which remained in place, but was uncertain of all that happened after that. He said he thought the bucket hit the cargo bay door, and "that's probably what broke its fall."