BOULDER, COLO., JULY 18 -- The Soviet Union has rejected the widely held belief that life does not exist on Mars and will make the search for life there a major part of its ambitious exploration of the Red Planet in the decade ahead.

That disclosure came during a four-hour satellite linkup today between Soviet scientists in Moscow and U.S. scientists here, and clearly startled some of the Americans, who believed that the U.S. Viking probes that landed on Mars more than 10 years ago had shown that no life exists on Mars.

During the extraordinary conference today, it became clear that the Soviets think that the Viking spacecraft may have looked in the wrong areas.

"We couldn't get them off the subject," said Chris McKay, a biologist with the National Aeronautics and Space Administration's Ames Research Center in Mountain View, Calif., who participated in the conference. "They have a fixation in their minds on life existing on Mars."

The Soviet participants in the conference repeatedly quizzed American scientists about areas of the planet that they thought would be most likely to sustain life, and they referred to the possibility of an underground "oasis" there.

Soviet missions scheduled to travel to Mars early in the 1990s will carry devices to search for microorganisms that may exist below the ground, which resembles the permafrost that blankets northern reaches of the Soviet Union.

About 25 scientists in each location took part in the satellite conference, held at the University of Colorado and sponsored by the Planetary Society of Pasadena. The purpose of the conference, hosted by Cornell University astronomer Carl Sagan, was to promote the concept of a joint U.S.-Soviet mission to Mars. That goal was clearly upstaged, however, by discussion of the Soviets' own plans for a search for life on Mars.

The Soviet Union has previously announced a wide range of unmanned missions to Mars during the 1990s, including a spacecraft that would scoop up rocks and return them to Earth for examination.

But few American scientists realized until today that a major goal of that program would be to address again the question of life on Mars.

Since the Viking probes, which landed in 1976, failed to turn up any evidence of life in two locations on Mars, nearly all U.S. scientists had concluded that if life ever did exist there, it is now extinct.

Although most American scientists who took part in the session said that they doubted that the Soviets would be successful, others sided with the Soviets.

"This is probably going to get me banned from ever participating in this kind of program again, but you did not prove there is no life on Mars by Viking," Carol Stoker of Ames told fellow scientists.

"They {the Soviets} accept the Viking results for what they were," added Chuck Klein, also of Ames. "They {the Viking missions} showed there is no life in two places. Now, they {the Soviets} are going to go to more interesting places."