CAPE CANAVERAL, AUG. 25 -- NASA's silent Mars Observer probe, which could be lost in space, destroyed or possibly wheeling around the Red Planet with a broken radio, missed a final deadline to contact Earth today, increasing concern that the $1 billion mission could end up a total failure.

"Unfortunately, we still have no two-way communication or one-way communication or data of any kind from the spacecraft," said project manager Glenn Cunningham. "I'm sorry to have to report that. We continue, however, with increased vigor in trying to reestablish communications."

Controllers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., lost contact with Mars Observer Saturday during a procedure to pressurize the probe's fuel tanks for a critical rocket firing Tuesday to put the spacecraft in orbit around Mars.

Initial efforts to reestablish communications were unsuccessful and no one knows whether the spacecraft exploded or tumbled out of control during fuel-tank pressurization, whether it went into orbit as it was programmed to do or whether it sailed on past Mars into a long orbit around the sun.

Based on an engineering analysis of propulsion system components, Cunningham said today he believes the spacecraft did not explode, but "I have no data and I can't really speculate beyond that."

Assuming it did not blow up, the solar-powered spacecraft, first American mission to Mars in 17 years, was programmed to go into an "emergency contingency mode" if five days passed without contact. That procedure would have required it to locate the sun, reset its radio gear and then aim its secondary radio antenna in the general direction of Earth and await instructions.

Flight controllers sent those instructions this afternoon when the five-day deadline ran out. And to their dismay, Mars Observer remained mute, its fate a complete mystery. While engineers will continue efforts to regain contact, the prognosis was not encouraging.

"The current situation, without communications, certainly erodes our prospects considerably," Cunningham said. "Every day, in fact, without communications clearly lessens our probability of success."

If contact eventually can be reestablished, and if the Observer is, in fact, in orbit around Mars, the mission to map the Red Planet and gather priceless data about its structure, composition and atmosphere likely could proceed as planned.

But if controllers ultimately discover the probe passed Mars without firing its braking rockets and continued on in an orbit around the sun, the mission would face a major delay and significant replanning.

In that case, the spacecraft would return to the vicinity of Mars sometime next year or in 1995. Assuming contact can be restored at some point and the problem corrected, engineers would be able to fine-tune the trajectory to put the spacecraft in the desired orbit around Mars, albeit much later than originally planned.

"If we're not in orbit, there are several options for making changes that would return the spacecraft to the vicinity of Mars," Cunningham said.

In the meantime, scientists say the loss of Mars Observer would be a major setback for American planetary exploration. Mission scientist Arden Albee said the flight was designed "to gather an immense amount of information about Mars."

"When humans go to Mars for the first time, they will have used the charts and the data and the information that Mars Observer {was built to} gather," he said. "If Mars Observer should fail, then we would have to re-do Mars Observer sometime in the near future."

Closer to home, the possible demise of Mars Observer, coupled with the Aug. 21 failure of a new $67 million weather satellite and problems afflicting the Hubble Space Telescope and NASA's Galileo Jupiter probe, likely will have an impact on the agency's budget battles in Congress.

"I'm sure," said John Logsdon, a space policy analyst at George Washington University, "there will be some sort of congressional firestorm that says, 'How in the hell can we waste a billion dollars? And now you're asking us to commit $10 billion over the next five years to space station?' I think the program is indeed in jeopardy."

Some observers believe the loss of Mars Observer might also rekindle debate about the wisdom of building big, complex and expensive spacecraft instead of smaller, cheaper probes that do not wreck a program when a failure occurs.

"I think it all goes back to the idea that this is how the NASA bureaucracy is geared -- you do big things, you have big spectaculars," said Joan Johnson-Freese, a space analyst with the Air War College at Maxwell Air Force Base in Alabama.

"Who pays any attention to the little package deals? Nobody," she said. "You go for flybys of Saturn, you go for a Mars Observer, things that will get media attention. Unfortunately, that sometimes backfires when the engineering glitch occurs. And this is what you get."

The $1 billion Mars Observer originally was designed to study the geology, weather and climate of the Red Planet.

1) Launched on Titan III in September 1992.

2) Cruise to Mars lasted nearly one year.

3) Was supposed to attain orbit at Mars this week.

4) Supposed to observe Mars from mapping orbit for one Martian year (687 days).

SOURCE: National Aeronautics and Space Administration.