Defense Secretary Caspar W. Weinberger yesterday called the president's "Star Wars" research program "necessary as a prudent hedge" against the "ominous possibility of a deliberate, rapid, unilateral Soviet deployment of strategic defenses."

Speaking to an American Society of Newspaper Editors luncheon, the defense secretary put new emphasis on the prospect that the Soviet Union might develop a space-based defense ahead of the U.S. Strategic Defense Initiative and "undermine the essential East-West military balance."

Weinberger appeared to return to arguments made by earlier administrations that ballistic missile defense research money was needed as a hedge against the Soviets developing a ground-based nationwide antiballistic missile (ABM) system.

Since President Reagan's initial March 23, 1983, speech outlining the program, administration officials primarily have defended the SDI research as a Reagan initiative aimed at making strategic missiles impotent, seldom mentioning a similar Soviet program.

Six days after he made his SDI speech, the president suggested in an interview that if U.S. research developed a viable defensive system, a future president might "offer it" to the Soviets.

More recently, however, as approval of SDI research funds has run into trouble in Congress, administration spokesmen increasingly have talked of Soviet laser and particle beam research and the possibilities of a Soviet defensive system.

Weinberger yesterday went further and speculated that Moscow may only agree to deep reductions in strategic offensive missiles "when their own strategic defense is deployed." He said, "If we have [our SDI] ready, then SDI may eventually provide mankind with the means to a safer basis for deterring aggression and ensuring world stability."

A Pentagon spokesman, after consulting with Weinberger, said the defense secretary had not intended to break any new ground and that the prospect that the United States is in a race with the Soviets to develop a space-age missile defense was "inherent" in statements he had made before.

Weinberger called SDI a "noble quest" and told the editors he wants their help "in clearing up misconceptions about strategic defense."

In dealing with criticism of SDI as "destabilizing," he said that "ongoing Soviet strategic defense activities would, in all likelihood, be far more destabilizing and far more threatening to Western security interests than our present research."

He also said that SDI enhances both arms control and allied security. A successful strategic defense system, he said, "could help carry the arms reduction process forward to even deeper reductions, and eventually to the goal of nuclear disarmament."

It would aid the NATO allies by reducing Soviet ability to destroy through nuclear weapons "those facilities essential to a conventional defense," he said.

The administration has been putting new arguments forward for the Star Wars program, according to one congressional aide in the defense area, because "it faces tough opposition to its SDI funding program." Raising the notion that the United States is in a race with the Soviets to get a Star Wars defense, he said, "might help on Capitol Hill."

Last year, the request for $1.7 billion was cut to $1.4 billion. The president is seeking $3.7 billion for next year. The Senate Armed Services Committee, the most sympathetic panel to the program, cut it $300 million last week.

"It will be cut below $2 billion in the House," one member said.

Administration officials testified last year that at least five years of research costing $26 billion would be needed to enable the next president in the early 1990s to decide whether a defensive system is possible.

If Congress substantially reduces the president's request, it would stretch a possible decision even farther into the future.