Astronauts Jack R. Lousma and C. Gordon Fullerton lost three of their main radio links with Earth today but switched to alternate lines of communication and pressed on with their scheduled seven-day flight aboard the space shuttle Columbia.

"As far as I'm concerned, this mission will go full duration," Gene Kranz, deputy flight operations director of the Johnson Space Center, said late today.

"It will take a few adjustments on our part, but I have no doubts we can fly safely in this backup mode of communication," he added.

Lousma and Fullerton lost three instant radio links through the shuttle's two transponders, which lock onto radio signals from the ground, amplify them in space, then amplify them again to beam an even stronger signal to Earth.

The transponders carry almost all of the information on the state of the shuttle's health and its speed and whereabouts in space.

But they carry very little voice transmission, which moves over two ultrahigh-frequency radio channels.

Voice transmission was still working normally today.

Lousma and Fullerton can hear everything said to them by controllers here, and the controllers have had no trouble hearing the astronauts' transmissions from any point in orbit.

The transponders work on two frequencies, one on high power and the other on low power.

One of the two is working on high power and being used to transmit information on Columbia's health and whereabouts and to receive ground commands that are stored in its onboard computer.

Columbia has two FM radio links that store information on tape recorders aboard and relay the information to Earth on command from the ground whenever flight directors decide they want the data.

These FM frequencies are receiving ground commands and storing them on the same recorders used to relay information to Earth.

Kranz said the flight plan could change if the high-power communication link on the working transponder is lost.

That would mean the state of the shuttle's health and its position could be transmitted to Earth only through the FM system after being recorded on tape.

Flight directors here thus would not have instant access to information about the shuttle and might want to terminate the mission rather than risk continuing the flight without such access.

Late tonight, Columbia was still using its remaining transponder link, its backup UHF voice line and its FM radio line employing tape recorders to relay information to Earth. Flight directors said the flight still had not been impeded by breakdowns in the prime radio communications.

"We are not bringing this flight home early because we've encountered a few problems," flight director Harold Draughon said tonight. "We have thermal tests to do and scientific tests to do. We want to fly this vehicle as long as we think it's safe, and we think it's still safe to fly."

If the shuttle were ordered home before its scheduled landing at 1:27 p.m. (EST) Monday, Lousma and Fullerton would have to touch down at an alternate landing site in California or Florida instead of the main site they are now targeted for at White Sands Missile Range in southern New Mexico.

Weather at White Sands worsened today and was expected to be even worse Saturday. A cold front brought overcast skies and high winds that blew dust across the two runways and created haze thick enough to obscure the landing site.

The Saturday forecast calls for more wind, gusting to 25 knots. That would be considered unacceptable for landing.

"The front is expected to pass by about 6 p.m. Saturday when the weather will begin to clear and winds will die down. Monday's weather will be mostly fair and mild, with light to breezy winds," the forecast said.

If Columbia is forced down at either Edwards Air Force Base in California or the Kennedy Space Center at Cape Canaveral, Fla., Lousma and Fullerton must land the 100-ton shuttle on concrete runways no longer than three miles and no wider than 100 yards.

Flight directors do not believe that Columbia's two test flights have produced enough information about its landing aerodynamics to allow a safe landing on such short and narrow runways.

Flight directors want the luxury of runways such as the seven-mile desert strip that also is wide enough to allow landings in crosswinds.

Monday's landing had been scheduled at Edwards, where Columbia touched down after its first two flights, but heavy spring rains have made the base's dry lakebed runways too muddy for a safe landing.

The transponder failures occurred Thursday night less than four hours apart when the spacecraft was over the Pacific Ocean.

The first failure took place just before the astronauts went to sleep and the second after they had gone to sleep, and they were not told of the second failure until today