The Mars Climate Orbiter was apparently destroyed early yesterday when the probe swept too close to the Red Planet during an attempt to go into orbit there, stunned and exhausted NASA officials said.

"I'm sorry to report that we have a serious problem with the Mars Climate Orbiter," Carl Pilcher, NASA's chief of solar system exploration, told reporters. "We may, in fact, be facing a loss of mission."

The spacecraft most likely broke up or burned up when it plowed into the thin Martian atmosphere, reported flight controllers at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., which manages most interplanetary missions for NASA.

If a navigation error was in fact the cause of the loss, this would represent an unprecedented failure for a JPL team that leads the world in aiming spacecraft through tiny, moving bull's-eyes hundreds of millions, or billions, of miles distant in space.

"We are, to put it bluntly . . . surprised," said mission manager Richard Cook of JPL.

NASA immediately formed a special task force, including some outside specialists, to investigate the mishap. Controllers used NASA's global network of giant radio antennas to continue scanning the skies for any signal from the $125 million spacecraft, in the waning hope that it had survived.

The orbiter was to have served as a communications relay for its sister spacecraft, the Mars Polar Lander, scheduled to arrive on the Martian surface Dec. 3 to search for signs of water ice at a site about 500 miles from the south pole. (The lander and orbiter together with their launches constitute a $357 million package.)

However, managers said, there will be no loss of scientific return from the landing craft because mission planners provided two other routes by which the data can be transmitted to Earth. One is direct transmission from the surface; the other is a relay through the Mars Global Surveyor, a research craft orbiting the planet. The lander's transmissions will take more time, without the planned high-speed linkup.

But the orbiter's planned research will be delayed for perhaps a decade, officials said. Following its service to the landing mission, it was to have spent a Martian year (687 days) operating in effect as the first Martian weather satellite, sending back daily information and images on temperature, dust and water vapor levels and cloud formation.

This is the latest in a series of failed missions to Mars from the United States and Russia, most notably including the loss of NASA's $1 billion Mars Observer in 1993 because of a ruptured fuel line. The much less expensive orbiter that went missing yesterday, part of NASA's new "smaller, faster, cheaper" approach to space exploration, was carrying a duplicate of an instrument designed for the lost Observer.

Flight controllers lost contact with the orbiter at about 5:06 a.m. EDT, just minutes after the spacecraft fired its main engine to slow down and enter orbit and just as it passed "behind" the planet as seen from Earth. They had expected to regain communications with the craft at 5:25 a.m., when it emerged from behind Mars, and begin a process called aerobraking, a fuel-saving method that uses carefully gauged passes through the atmosphere to maneuver into the desired final orbit.

The orbiter was supposed to approach at an altitude no lower than 87 miles above the surface. Instead, according to Cook, controllers realized belatedly that the trajectory had "dropped" to an altitude of about 37 miles, most likely sending the craft directly into the stressing forces of the thin Martian atmosphere. The minimum survivable altitude is thought to be about 53 miles.

Controllers had virtually ruled out any mechanical problems aboard the spacecraft as the culprit, he said, and were focusing on either human error or a software problem in JPL's navigation operation.

The missing spacecraft was one of 20 science missions NASA has launched in the last two years and, along with the lander, represented the second wave in a planned 12-year assault on the secrets of the Red Planet. The theme of the exploration is the search for water, as key to understanding whether life exists, or has ever existed, anywhere on Mars.