When the full Senate begins debating next year's space program budget on Monday, the failure of the Mars Observer last month will undoubtedly be raised. True, the probe's disappearance cost taxpayers $l billion and rendered worthless years of scientific work. But Americans must not let it extinguish their already dimming enthusiasm for space exploration.

Since the 1969 moon landing, the National Aeronautics and Space Administration has been afraid to commit itself to a single overarching, long-term goal. It should use the Mars Observer disaster to refocus itself. First, money that would have been used to analyze the Observer's data should go to build a better Mars probe—the Defense Department's Clemenline satellite could be readied for a Mars mission in two or three years.

Then the agency should re-emphasize manned exploration—this months decision to virtually merge the U.S. and Russian programs will make manned missions much less expensive. The redesigned space station Freedom is the key. Despite claims about the station's usefulness in medical and scientific experiments and for manufacturing purposes, it is obvious that its main justification should be to prepare for the exploration of Mars.

With Mars as the logical objective, how do we start? A manned landing on the Martian surface is too costly a first step. The simplest project would be a manned fly-by of the planet, but a two-year flight that puts astronauts near Mars for only a few hours would not be very cost-effective.

A manned space laboratory orbiting Mars for weeks or months — without landing — would give the highest benefit for the least cost, particularly if it were anchored to either of the stable Martian moonlets, Phobos or Deimos. It would cost less than 10 percent of the $400 billion figure for Mars exploration bandied about in the Bush Administration because it would not need the complicated propulsion systems that allow a manned craft to enter and leave the red planet's atmosphere.

The space lab would be close enough to drive remote-controlled rover vehicles on Mars's surface to gather data and collect samples to be analyzed at the lab while still fresh. All this could be done without exposing humans to the dangerous Martian terrain.

These studies could not be done as effectively with unmanned spacecrafts and robotic rovers controlled by scientists on Earth. The delays are too long; it takes about an hour for a control signal to make the nip from Earth to Mars, and it would take a year or more for a sample to be returned.

A rich scientific hat vest awaits us, including data on the origin and geologic evolution of Mars, as well as information on the climate changes that transformed a warm and wet Earth-like planet into a dry, cold one. A new discipline would emerge: comparative planetology.

The origin of Phobos and Deimos is another mystery. Are the tiny moons captured asteroids or are they leftover material from the formation of Mars? And the moons may yield important raw materials, possibly the basis for manufacturing rocket fuels and other useful substances. The holy grail, of course, is the discovery of life forms or fossils that might exist below the dry surface of Mars or in the moist margins of the ice caps.

Inevitably, manned exploration and habitation of the red planet would follow. There are even plans afoot for "terraforming" the Martian atmosphere to make it livable for earthlings. It would be tragic if the setbacks and mistakes of the last 20 years dampened the Senate's enthusiasm for the great human adventure of space exploration.

S. Fred Singer, professor at the Institute for Space Science and Technology in Gainesville, Fla., directs the Science and Environmental Policy Project.