SCIENCE PANEL URGES CAUTION IN HANDLING MARTIAN SAMPLES.

Byline: Warren E. Leary The New York Times

It has been the basis of many science fiction stories: The rocket returning from Mars carries an unknown organism destined to cause havoc on the Earth.

A panel of scientists convened by the National Research Council warned the National Aeronautics and Space Administration on Thursday that although this is unlikely, it is possible. Plans to send robot spacecraft to Mars to bring back soil samples should include stringent precautions to prevent contaminating the Earth with alien organisms, the scientists said.

The 12-member committee's report said that even if microorganisms exist on Mars and hitch a ride back to Earth, ``the likelihood that they could survive and grow and produce harmful effects is judged to be low.'' It is unlikely that Martian germs could compete successfully with Earth organisms, which are better adapted to their habitats on Earth, it said.

``Contamination of Earth by putative Martian microorganisms is unlikely to pose a risk of significant ecological impact or other significant harmful effects,'' the panel said in a report. ``The risk is not zero, however.''

``It is reasonable that NASA adopt a prudent approach, erring on the side of caution and safety,'' it said. ``Samples returned from Mars by spacecraft should be contained and treated as though potentially hazardous until proven otherwise.''

There has been renewed interest in exploring Mars since August, when NASA scientists announced finding signs of possible microscopic life in a meteorite found in Antarctica 13 years ago. The meteorite, believed to be a piece of Mars blasted into space by impacts on the Martian surface, contained shapes that resembled fossilized microbes and chemicals that could have been produced by bacteria.

NASA is making plans for a mission to send back a sample in the middle of the next decade, after first launching a series of spacecraft to the Red Planet every two years. These earlier missions, including the Mars Global Surveyor and the Mars Pathfinder now en route, will help find the best places from which to take samples that may contain life.

The cold, barren surface of Mars is too inhospitable to harbor life as we understand it on Earth, the new report said, but patches of living matter might exist in areas of active volcanism or water-ice if either is discovered on the planet.

``If life forms ever existed on Mars, either by having been formed in an independent origin or having been transferred there from Earth, it is possible that they have continued to exist up to the present time,'' the report said.