FOR years, the handwriting on the wall at National Aeronautics and Space Administration headquarters has conveyed a simple message - less is more. Fiscal reality excludes budget-hogging projects. Space scientists would prefer a variety of smaller missions to a few grandiose programs.Senior NASA officials have finally seen the message. After heated debates this summer, they reportedly are ready to emphasize smaller, less costly missions. NASA is bowing to the inevitable. Failures in the past half decade - including the Challenger disaster - highlight the risks of putting too many space effort "eggs" in a few "baskets." Anxiety over malfunctions in the Hubble telescope's control system has joined disappointment over its flawed mirror. The Galileo spacecraft's stuck antenna threatens to ruin the billion-dollar Jupiter mission. Meanwhile, the cost of even the scaled-down version of space station Freedom continues to squeeze space science. Yet the Freedom program lacks a clearly defined purpose with a potential payoff large enough to compensate for that cost. NASA's plan to base its Earth Observing System (EOS) on a few super-satellites has run into similar risk and cost-benefit criticism. It is indeed time for "dramatic change" in NASA planning. The agency should take a truly fresh look at United States space goals and the strategy for meeting them. Space station Freedom should be scrapped unless a new compelling reason can be found to carry it forward. The same holds true for the platforms planned for the EOS system. The 1990s could be a decade in which the United States shapes a space program it can afford. Such a program could return more space science dividends through a smaller but consistent effort than the present emphasis on costly major projects realistically can promise.