The first launch in two years of the flagship space shuttle Columbia was scrubbed yesterday when a hydraulic pump driving one of Columbia's main steering mechanisms went out of control 15 seconds before liftoff.

The launch of Columbia and a seven-man crew that includes Rep. Bill Nelson (D-Fla.) was rescheduled to "no earlier than" Jan. 4. The new date was picked to give shuttle workers time off for the holidays, to avoid paying the Air Force to keep open its Eastern Test Range at Florida's Cape Canaveral, and to avoid paying launch pad workers triple-time pay for working between Christmas and New Year's.

"It probably goes without saying we're somewhat disappointed not to have launched today," Columbia Commander Robert L. Gibson, a Navy commander, said after the launch was called off at 7:54 a.m. "We thought we were all done with our Christmas shopping but now we have a couple of days left to do some more."

The scrub was blamed on a high-speed turbine in one of Columbia's two towering solid rocket motors that helps steer the shuttle as it climbs off the launch pad during its first two minutes of flight.

The hydraulic steering mechanism has a backup in case it fails in flight but mission rules call for an automatic abort if the prime steering system fails before liftoff.

NASA officials said fail-safe mechanisms detected the faulty turbine spinning at 86,000 rpm, which exceeded the turbine's "red line" limits by almost 7,000 rpm. Shuttle Operations Director Robert Sieck said the turbine would have to be removed and either repaired or replaced, a procedure that will not involve moving Columbia back from the launch pad but one that will take at least until Christmas.

"We'd promised the launch team time off between Christmas and New Year's and they'll get that time off," Sieck said. "They deserve it."

If Columbia had left Earth yesterday, it would have been the 24th space shuttle flight in more than four years and 10th shuttle flight this year, a doubling of the previous record.

The first of the four-shuttle fleet to fly, Columbia has not been in service since 1983 when it was put in the shop for extensive cockpit and electronic modifications.

Yesterday was the third time in four years that a scrub was called in the last 20 seconds of the countdown. On June 26, 1984, Discovery's maiden liftoff ended with an engine shutdown on the pad and on July 12 of this year Challenger suffered the same kind of shutdown.