The Mars Observer is a spacecraft designed to map our neighboring planet in exquisite detail. NASA spent $1 billion but failed to make the mission foolproof. In August, just as the delicate craft neared its target, some accident disabled its communications gear, probably condemning it to snap endless postcards of Martian vistas that no one will ever admire.

The futile outcome mirrors the general state of space exploration, which also has come far with little to show. The universe is waiting, but NASA can think solely of plumbing and aluminum, the chief ingredients of its much-redesigned space station. The project's only evident purpose is to make work for space contractors and NASA's erratic fleet of space shuttles. Its feeding has long starved the agency's more promising ventures.

Thus, the Hubble Space Telescope, designed to peer back close to the universe's edges and the dawn of time, was put into orbit with a flawed mirror and dishearteningly fuzzy vision. The Galileo spacecraft, now en route from Earth to Jupiter, cannot report the full wonders of its journey because its main antenna won't unfurl.

These failures could not come at a worse time for space exploration and its supporters. There is no longer any urgency to beat the Soviet Union to the moon or Mars. NASA cannot claim that it spins off critical technology for industry, which surpassed it years ago in materials and computers. Viewers have tired of astronauts' weightless and often witless antics in space.

Given its recent performance, shouldn't NASA be retired and its $15 billion annual budget be put to better uses?

Suppose for a moment that there were no NASA, no enormous investment in the clunky hardware of manned spaceflight. Would we need to venture into space? What arguments could anyone make for starting a new civilian space agency from scratch?

One is that there's a lot out there to be discovered. The solar system holds amazements that we have only begun to sample, from the watery blue orb of Neptune, a giant bubble floating in the twilit edges of the sun's demesne, to the tiny shepherd moons that tend the rings of Saturn. "And since, my soul, we cannot fly/To Saturn nor to Mercury," concludes a Housman poem I had to learn for some schoolboy offense, "Keep we must, if keep we can,/These foreign laws of God and man." Missions that record these extraterrestrial geographies offer escape, even if only in imagination, from laws, conventions and the banal.

Besides discovery, another reason to go to space is what might be called the insurance option. Aren't two planets better than one? Mars is probably the least difficult place in the solar system to make hospitable. But it would take decades to get ready, so those who foresee a human settlement of Mars urge starting soon. As our planet edges ever closer to its carrying capacity, Mal thusians could one day prove right for a change, especially if there should be some sudden shift in the conditions for agriculture. What if the long- threatened greenhouse effect at last arrives?

There's also the matter of historical imperative. Humankind will inevitably spread beyond Earth to exploit the opportunities of the solar system, this argument goes. So why not start soonest, lest later generations judge us faint hearts who faltered at a decisive turning point in history? "Like the Alexandrian Greeks, who discovered the motive power of steam but used it to open temple doors instead of initiating an industrial revolution in the first century A.D.," some future Gibbon may scold, "Americans of the late 20th century first reached the moon but then turned back home, too discouraged by the vastnesses ahead to grasp the new worlds they had brought within reach."

Then there is the agenda of science. Origins are among its most intriguing questions. But many of the answers now seem to lie beyond Earth's boundaries. The geology of other planets may bear the records, long erased from Earth's, about the conditions that prevailed when life began. The solar system surely holds clues as to whether the first chemical building blocks of life, or even the seeds of life itself, arrived aboard meteorites to fecundate the primitive Earth. Since it now seems that the stately process of evolution was brusquely diverted from time to time by asteroids or comets that wandered into collisions with Earth, there is much to learn about the history of these celestial visitations.

Gaining scientific knowledge is perhaps the most tangible reason for a serious and immediate space program. Research with no practical purpose in view is an accepted function of government, not least because it often yields unexpected gains. Planetary exploration is not cheap, but if abolishing crime and poverty were the preconditions for anything of lesser priority, governments would never subsidize opera, protect the landscape or hunt for quarks. And space exploration is the kind of thing governments do well. Project Apollo, to land men on the moon, was a brilliant success; had the nearly $25 billion it cost been poured into social programs, where money is seldom decisive, the results would have disappeared long ago.

Grant, then, that a civilian space effort of some size is warranted. A magnificent space program could be mounted for something closer to $5 billion a year, instead of $15 billion as at present, simply by keeping people on the ground and sending computer-driven vehicles to roam the solar system. It's providing for astronauts' safety that takes up the lion's share of NASA's budget. Though humans may live beyond Earth some day, no logical program requires them to do so this soon.

It's even possible to imagine a space program that would cost almost nothing. The Department of Energy has on its payroll several outstanding national laboratories with nothing much to do now that nuclear power is in eclipse and the cold war over. At Los Alamos and Livermore, two of the world's finest teams of physicists and engineers are desperately looking for a worthy intellectual challenge now that the development of nuclear weapons has pretty much achieved perfection. Let the two labs compete in building spacecraft as vigorously as they once did in designing nuclear warheads. Their scientists would embrace the challenge, and their skills would produce superb machines for exploring the mysteries that lie beyond Earth.

Recently, the Galileo, crippled as it is, radioed back a snapshot of a passing asteroid known as Ida in the astronomers' catalogues. Shaped like an Easter Island statue, with a meteor crater for an eye socket, it stretches 32 miles from crown to chin. To some, Ida may look like just another rock; to astronomers, it is an untouched piece of the solar system's building material, the dust of stars that died before the sun was born. Next July, Galileo should witness an eye-catching series of multimegaton explosions as the pieces of a stricken comet plow into the red clouds of Jupiter.

For 20 years, NASA's political masters in the White House and Congress have let the agency drift. One day, maybe, something will rekindle the desire to explore and understand.