Is the United States serious about sending a manned mission to Mars? If so, let us get on with Space Station Freedom. If not, let us fall back and reconsider. At the risk of being charged with a flat-Earth lack of vision, I suggest we fall back and take a fresh look.

In 1984 Congress approved the concept of a space station that would remain in orbit for at least 30 years after its assembly. The project was sold primarily as an investment in scientific research that would pay rich dividends in civilian spinoffs. The first estimated price tag was $8 billion in 1984 dollars, but the figure was grossly misleading.Now the estimates of cost have floated into an orbit of their own. In testimony before a House subcommittee on May 1, we heard the kind of figures that Rep. Bob Walker, R-Pa., calls "funny numbers." The National Aeronautics and Space Administration put the initial cost at $30 billion in 1991 dollars. The subcommittee staff hazarded a guess of $52 billion. The General Accounting Office pessimistically predicted $118 billion over the 30-year period. One witness said $180 billion.

What would the taxpayers get for these astronomical sums? Tangibly speaking, not much. Under congressional prodding, NASA has cut back the original concept. As it now stands, Freedom would support a crew not of eight, but of only four. Its costly laboratory would serve only two areas of scientific experiment: microgravity and life sciences.

Harvard's Professor Nicolaas Bloembergen, president of the American Physical Society, testified that a manned space station "is unsuited to microgravity research." The trouble is that "each movement by an astronaut would shift the center of mass of the station, producing a momentary acceleration which is equivalent to gravity." Other witnesses before the committee voiced the same opinion.

What, then, of research in the life sciences? Yes, the experts agreed, a manned long-orbiting space station will indeed be required if - if we intend to go for Mars. In short, to quote Bloembergen again, "the only reason for putting humans into space is to learn how to put more humans into space." Could we learn what we need to know about Mars by sending robots instead?

During floor debate on May 2, speakers recalled John F. Kennedy's analogy: Space is "the new ocean." We cannot let it go unexplored. The vision of space travel is a captivating vision.

But the hard question remains: Is this particular investment the best way in which to continue the explorations of our solar system? Some highly qualified observers are highly doubtful.

For my own part, I am wedded to the idea of exploring this "new ocean." But I have read the record and listened to debate. This particular investment strikes me as a bad investment.