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Russian space managers have changed the makeup of a two-man cosmonaut crew on standby for a flight to the abandoned Mir space station in the event of any future emergency that might cause an uncontrolled re-entry.

Commander Salizhan Sharipov and flight engineer Pavel Vinogradov had been in training for a potential flight to Mir, which is scheduled to be deorbited in late February, but they have been replaced, NASA sources said today.

The ITAR-TASS news agency reported Tuesday the new crew is made up of commander Gennady Padalka, a Mir veteran, and flight engineer Nikolai Budarin, a Mir veteran who also flew aboard NASA's space shuttle.

A NASA source confirmed the crew change, but could not confirm the identities of the replacements.

But Padalka and Budarin trained extensively for a potential emergency flight to the international space station last year in case the Russian command module, Zvezda, was unable to dock with the outpost.

Zvezda and the space station made a normal linkup, however, and an emergency flight was not necessary. But given their previous training, Padalka and Budarin would appear to be well suited for any emergency flight to Mir.

No such flight to Mir is currently planned. The Russians plan to launch an unmanned Progress supply ship to Mir around Jan. 10. The Progress will be used to raise Mir's orbit slightly, setting up a controlled re-entry around Feb. 28.

But an emergency crew might be needed if major problems develop between now and then.

While the Russians have not announced an official reason for the crew swap, Sharipov told ITAR-TASS he was upset by the decision.

"We had been training for more than six months to act in emergencies," he told the news agency. "Everything was all right, but the (governmental) commission decided to change the crew."

Contact with the unmanned Russian Mir space station was briefly lost early today after a computer in the lab's motion control system allowed the station to drift out of its normal orientation, depleting on-board batteries.

During a subsequent pass over Russian ground stations, commands were uplinked to re-orient the station to maximize the amount of sunlight falling on Mir's solar arrays. Russian flight controllers told their NASA counterparts the station was well on the road to recovery.

It's not yet known what caused the motion control system computer, which was installed last summer, to allow the station's orientation to change in the first place. But engineers believe it was a "single event upset" type of event, i.e., some sort of one-time spurious command, and that Mir's systems appear generally healthy.

The brief scare, however, raised concern once again about the Russians' ability to control the abandoned station's upcoming re-entry and breakup.

The current plan calls for the launch of an unmanned Progress fuel tanker around Jan. 10 that would dock with Mir two days later. The Progress would be used first to raise Mir's orbit slightly to set it up for a controlled re-entry over the Pacific Ocean between Feb. 26 and 28.

But that assumes Russian flight controllers can communicate with the station and that its main central computer and motion control system are operational.

If contact was permanently lost, and if nothing else was done, Mir would re-enter the atmosphere and break up around the end of January, according to the latest NASA projections.

Debris from Mir is expected to survive the heat of atmospheric entry and impact Earth somewhere along the station's ground track. Mir's orbit carries it 51.6 degrees to either side of the equator where 70 percent of the world's population lives.

Two Russian cosmonauts - Salizhan Sharipov and Pavel Vinogradov - are trained to make an emergency flight to Mir if conditions warrant to make repairs or take over manual control of the station.

But it's not yet clear how soon they could be launched in a real emergency or even whether intermittent communications would warrant such a mission.

Russian engineers believe the glitch today occurred in a motion control system computer that was installed last year to control the station's attitude until the lab's main computer is reactivated for re-entry.