President Reagan said yesterday that research into a missile defense system could prompt both superpowers in the Geneva arms talks "to actually reduce" their nuclear arsenals because "by making missiles less effective, we make these weapons more negotiable."

The administration has said that deployment of a space missile defense system to knock out incoming nuclear warheads is far in the future. Reagan yesterday attempted to link the continuing research program with cuts in offensive missile arsenals at the Geneva negotiations.

In a speech to the National Space Club, Reagan also appeared to be answering critics who say that his Strategic Defense Initiative (SDI), or "Star Wars" missile defense system in space, would lead to a major expansion of offensive nuclear missiles on both sides.

"Far from being a violation of existing arms agreements, once our adversaries fully understand the goal of our research program, it will add new incentives to both sides in Geneva to actually reduce the number of nuclear weapons threatening mankind," he said.

"By making missiles less effective, we make these weapons more negotiable," he added. "If we are successful, the arms spiral will be a downward spiral, hopefully to the elimination of them."

Critics say that deployment of SDI would result in a new round of offensive missile expansion as the superpowers seek to overwhelm each other's defense systems. The administration has argued that a defensive system that renders many -- if not all -- missiles obsolete would make additional offensive missiles too costly to be worth the effort because fewer of them would get to their targets.

Reagan yesterday appeared to be carrying this argument further than he has before by saying that existing research into missile defense would create pressure for both sides to reduce their offensive arms now.

The president objected to the term "Star Wars" to describe his program but quoted from that popular film in defending it.

"The Strategic Defense Initiative has been labeled 'Star Wars' but it isn't about war. It's about peace," he said. "It isn't about retaliation, it's about prevention. It isn't about fear, it's about hope. And in that struggle -- if you'll pardon my stealing a film line -- the force is with us."

Reagan also announced the appointment of a new national commission on space to be chaired by Thomas O. Paine, a former head of the National Aeronautics and Space Administration and Northrop Corp. executive, saying the panel will "devise an aggressive civilian space agenda to carry America into the 21st century."

Reagan was awarded the Goddard Memorial Trophy by the space club, founded in 1958 after launch of the Soviet satellite Sputnik to advance U.S. "leadership" in rocketry and space. The award is named for pioneer rocket inventor Robert Goddard.

In his luncheon address at the Shoreham Hotel, Reagan said a missile defense system could "render obsolete the balance of terror" and "replace it with a system incapable of initiating armed conflict or causing mass destruction, yet effective in preventing war."

He said it "is not, and should never be misconstrued as, just another method of protecting missile silos," as some have suggested for the early stages of SDI deployment. Reagan also said an "essential element" of his research program is to defend the United States and its allies from long-range and intermediate-range ballistic missiles.

The Soviets repeatedly have made the space missile defense system their chief target in the Geneva talks. Secretary of State George P. Shultz said this week that the United States would negotiate with the Soviets before deploying a strategic defense, but "this does not mean giving the Soviets a veto" over it.

In addition to Paine, who is a high technology consultant, members of the new space commission include:

Laurel L. Wilkening, vice provost, University of Arizona; Luis W. Alvarez, physicist, Lawrence Berkeley Laboratory; Neil A. Armstrong, first man to walk on the moon and now chairman of Computer Technology Aviation Inc.; Paul Jerome Coleman, professor, UCLA, and assistant director, Los Alamos National Laboratory.

George Brooks Field, senior physicist at the Smithsonian Astrophysical Observatory and professor, Harvard; retired lieutenant general William H. Fitch, former deputy chief of staff for aviation, U.S. Marine Corps headquarters; Charles M. Herzfeld, vice president, ITT Corp.; J.L. Kerrebrock, professor, Massachusetts Institute of Technology.

Jeane J. Kirkpatrick, retiring U.S. ambasssador to the United Nations; Gerard K. O'Neill, chief executive, Geostar Corp., Princeton, N.J.; Kathryn D. Sullivan, astronaut and first woman to walk in space; David C. Webb, consultant and chairman, National Coordinating Committee for Space, and retired brigadier general Charles E. (Chuck) Yeager, U.S. Air Force, the first man to fly across the sound barrier.