Mars Probe Still Silent; Hopes Dim : Space: Critical moment passes with no signal from craft that it achieved planetary orbit. Scientists hold out faint hope that Observer quietly carried out maneuvers.

The Mars Observer, at the crucial moment in its 480-million-mile journey to Mars, ignored NASA’s furious commands Tuesday and may have missed its long-awaited appointment with the Red Planet.

NASA flight controllers had no way of knowing whether the planetary probe had safely reached a planned Martian orbit on its own or had vanished in the void between planets. Indeed they had nothing except a faith in their own human engineering skill to sustain the belief that the spacecraft still existed at all.

Engineers at Jet Propulsion Laboratory in Pasadena, which is running the mission, listened in vain through the antennas of the agency’s Deep Space Network for any sign of the lost space probe. There was only an ominous silence.

About 2:40 p.m.--the critical moment of the scheduled rendezvous with Mars--a silence fell over the tree-lined Pasadena space center. Attention centered on a simple computerized graph projected on television monitors throughout the JPL campus.

Any movement on the red, white and blue graph would have signaled the resumption of transmissions from the lost probe. After seven minutes of silence, the voice of the NASA flight controller crackled on the intercom: “We have come up negative in our search for a signal.

“We will continue the search.”

The flight controllers maintained their vigil throughout the evening Tuesday, like a coven of 19th-Century whaling widows refusing to relinquish hope for husbands lost at sea. But they could not stem growing suspicions that the probe might have been destroyed Saturday when it lost contact with Earth, where its journey began last September.

“I’d like to believe the spacecraft is in orbit around Mars. We will continue to try and re-establish communications with the spacecraft, assuming it is in orbit,” said NASA project manager Glenn E. Cunningham. “We will continue to do that as long as we have the resources. We are not giving up. I need to emphasize that very strongly,” he said.

The nearly $1-billion Mars Observer project was the first U.S. mission to the solar system’s mysterious fourth planet in 17 years, designed to pave the way for a new generation of international planetary exploration centered on Mars. After its insertion into orbit, it was to have conducted a comprehensive study of Mars, including transmitting daily weather reports, which scientists hoped would tell them something about why the planet no longer has water.

As the television monitors at JPL played prerecorded videotapes of lectures on the spacecraft’s science goals, NASA officials held out the faint hope late Tuesday that the Observer might have automatically performed the delicate series of rocket firings that would place it in the proper orbit.

NASA engineers and space scientists said the spacecraft--one of the most sophisticated and independent planetary probes ever designed--could still establish communications with Earth on its own this afternoon. Officials said there was a remote possibility that the Observer might have suspended operations in an emergency “safe” mode designed to conserve its systems whenever Earth-based transmitters fail.

If that is true, the probe will attempt to contact JPL no later than 2 p.m. PDT today--five days after it supposedly turned off its transmitter.

“Either it is going to come on the air after five days, or they all are going to get drunk,” said John Pike, director of the space policy project at the Federation of American Scientists.

“I think it’s gone,” said space historian James Oberg in Houston, who has written authoritatively on Mars and the missions to explore it during the past 30 years. Oberg said Tuesday that JPL officials “are really avoiding the fact that it was probably a catastrophic failure.”

When the spacecraft lost contact Saturday, it was preparing to pressurize its fuel tanks before commencing a series of scheduled orbital maneuvers. Oberg said he suspected the fuel tank simply exploded. “Something violent occurred during the blackout,” he said.

NASA project managers dismissed any suggestion that a fueling accident could have irreparably damaged the spacecraft. Cunningham said the likelihood that the tank burst was “less than one-tenth of 1%.”

In the meantime, NASA planners continued to frame exotic contingency plans for a spacecraft that independent space experts said may no longer exist. One plan suggests a yearlong detour around the sun for a second try at Mars.

“We have the very best people available working the problem,” said William Piotrowski, acting director of solar system exploration division at NASA headquarters in Washington. “We have confidence in the people and the system. We are going to keep trying to establish communication.”

Throughout much of the day Tuesday, JPL engineers suspended their efforts to transmit new commands to the spacecraft out of concern that they might interfere with the automatic orbit maneuvers. But when no signal was received from the probe, they expected to resume a series of electronic wake-up calls, which they had been sending every 20 minutes since Saturday night.

Asked how he felt about the continuing silence from the spacecraft, project scientist Arden Albee said, “Terrible. Terrible.” Cunningham said flight engineers were handling the tension by “screaming loudly.”

Flight system engineer Charles Whetsel stared at the motionless video computer display. “We are going to have another long night ahead of us,” he said.