By holding the federal budget to no real growth for the next five years, the deficit agreement sets up some fierce battles about which discretionary programs should rise and which should fall. Given the country's urgent needs for new investment -- in civilian technologies, education, infrastructure and energy efficiency, among other priorities -- the agreement means that many programs must be dropped completely, at least for the foreseeable future.

In the interest of making a constructive start in this painful process, I propose as an early candidate for the chopping block the administration's program to establish manned outposts on the Moon and Mars.

The plan is to build a large orbiting space station from which crews will be assembled and vehicles built, fueled and serviced for establishing a permanent base on the Moon, which in turn will serve as the launch point for colonization of Mars. The anticipated price tag for this -- through 2025 -- is, coincidentally, the size of the deficit reduction goal, $500 billion. Realistically, experience suggests that the actual cost would be at least double or triple that and probably much more.

The Moon-Mars program is the pet project of the National Space Council, chaired by Vice President Dan Quayle. Lest you think this just a harmless way of keeping the vice president occupied, the plan has been vigorously endorsed by both President Bush and budget director Richard Darman. The project will find plenty of champions on Capitol Hill as well. As the defense budget shrinks, the pressure grows to fill the gap for the aerospace contractors, whose ability to lobby Congress from every congressional district is to be taken seriously.

Darman made his case in a much ballyhooed speech last spring. The American example, he argues, is not just important, but nothing less than "fundamental to the pace of human progress and the ultimate quality of human life." It, in turn, depends both on our economic success and on "the inspirational quality" of our behavior. "The question of practical, ideological, even spiritual, interest is: How can we keep America No. 1?"

The answer to that one, it turns out, is to restore "the spirit of the American Romance," which in Darman's lexicon consists of some familiar fundamentals ("love of freedom, respect for individual rights, faith in the future"), mixed with some self-explanatory newcomers ("appreciation of markets") and spiced with a real puzzler, "the heroization of risk-taking."

Prudent risk-taking, one would have thought, is its own reward. But not, apparently, when so much is riding on the inspirational qualities of American investment. The single undertaking that meets that stiff test is -- you guessed it -- the Moon-Mars project. It alone "will symbolize directly what is at the heart of the American Romance: Man is meant to pioneer, to explore, to expand, to advance, to reach and exceed new frontiers."

If the goal is really to explore the cosmos and advance our knowledge of its mysteries, unmanned rather than manned exploration, which can penetrate longer, farther and deeper into space for a fraction of the cost, is the way to go.

On the other hand, there is no shortage of scientific frontiers here at home. We know less about the deep oceans than about the surface of the Moon and even, some would argue, than about the surface of Mars. It is not only children who wonder how clouds are formed -- atmospheric physicists still do too. We don't know to within a factor of 10 how many species share this planet with us, nor the potentially useful characteristics of those that become extinct daily.

There are any number of exciting technological challenges, as well. We could use a transportation system that gets us to work quickly and comfortably without making the air we breathe a health risk. We need (here's a modest one) substitutes for fossil fuels. We need agricultural systems vastly less reliant on toxic pesticides. The world could certainly use a safe, cheap, lasting and revocable contraceptive. And so on.

But I suspect that Darman had a different kind of frontier in mind. For most Americans, I'd guess, "frontier" conjures up wagon trains, laying the rails, opening the West, new opportunity and also, of course, leaving bad things behind. And here's where, I think, the arguments for not attempting to colonize the Moon and Mars become even more compelling than the fiscal realities.

We could, after all, afford this venture and many others if we chose to tax ourselves as we have in the past or as Europeans and Japanese do today. We are rich enough. But we shouldn't seriously consider the massive investment needed to leapfrog mankind onto other planets as long as our planet is in such a parlous condition. Forty thousand children die each day from malnutrition and disease. More than 1 billion people exist -- it cannot be called living -- in absolute poverty. Forests are burning, soils are turning white from salt, species are disappearing at an estimated rate of four per hour. The specter of greenhouse warming casts an ominous shadow over our future.

All of these trends can be reversed. But that will cost plenty of money. The trick will merely be to convince ourselves that this is as noble -- as inspirational -- an endeavor, worthy of mankind's greatest effort, as starting over again on Mars. The writer is vice president of the World Resources Institute.