President Reagan yesterday offered to negotiate with the Soviet Union a revised arms agreement in which the United States would "substantially reduce" the number of Pershing II and cruise missiles intended for deployment in Europe if the Soviets agree to scrap part of their already installed missile arsenal.

The president said his ultimate goal was still to eliminate all intermediate-range nuclear weapons in Europe. Aides also said that only such a "zero-zero" agreement would prevent the U.S. deployments from starting as scheduled in December.

"When it comes to intermediate nuclear missiles in Europe, it would be better to have none than to have some," Reagan said in a nationally televised statement. "But if there must be some, it is better to have few than to have many."

The new proposal was presented to the Soviets at Geneva on Tuesday by the chief U.S. arms-control negotiator, Paul H. Nitze. Its public announcement yesterday was welcomed in Congress as a significant step.

The president was deliberately vague about the number of missiles that should be permitted by an interim pact. Officials said his strategy is to prod the Soviets to come up with an acceptable number and, failing that, to put Moscow at a disadvantage in the battle for public opinion in western Europe.

Furthermore, authoritative sources indicated that if the Soviets do not suggest some interim level of missiles or warheads the United States would offer a specific number of warheads--roughly 300 on each side--as a starting point for negotiations.

That proposal probably would come before the next round of talks begins in Geneva on May 17, they said.

Such a move, officials acknowledged, is also part of a strategy for a series of actions throughout the year to sustain the idea that the United States is more flexible than the Soviets in seeking an accord.

The intent is to help defuse anticipated demonstrations in western Europe later this year against the U.S. missile deployments and to help allied leaders muster public support for the deployments.

The president and his chief advisers say they believe that the Soviets respond most readily to a threat of force, and say they are convinced that serious negotiations are likely only after the deployment of Pershings in West Germany and cruise missiles in Great Britain and Italy begins in December. Belgium and the Netherlands are scheduled to receive missiles later.

"If we were to reach an agreement on equal levels of warheads, we would still begin deployment at the end of 1983," said a senior administration official who briefed reporters at the White House before the president spoke.

"We believe that it is only the deployment date and the beginning of deployment that gives the Soviet Union any incentive whatsoever to negotiate in Geneva," the official said.

Speaking to an audience of NATO ambassadors in the East Room, Reagan emphasized that his administration "consulted intensively" with allies before making the interim proposal.

In fact, the U.S. proposal was in many respects a response to the concern of allied leaders who, anticipating demonstrations protesting the missile deployment, publicly urged Reagan to demonstrate flexibility about his original "zero-zero" proposal.

Reagan called the consultation "a model for how an alliance of free and democratic nations can and must work together on critical issues."

But the administration's hope for a positive Soviet response is not high, officials said.

They pointed to recent statements of Soviet leader Yuri V. Andropov denouncing Reagan, and they reiterated the familiar point that it is deployment that will produce serious negotiations.

However, the president in his public statement did not attempt to pre-judge the outcome.

"If the Soviets will not now agree to the total elimination of these weapons, I hope they will at least join us in an interim agreement that would substantially reduce these forces to equal levels on both sides," Reagan said.

" . . . Ambassador Nitze has explained that the United States views this proposal as a serious initial step toward the total elimination of this class of weapons, and he has conveyed my hope that the Soviet Union will join us in this view. Our proposal for the entire elimination of these systems remains on the table," the president added.

The Soviets have deployed 351 modern SS20 missiles, each with three warheads, and about 200 older SS4 and SS5 missiles.

The United States plans to deploy 464 cruise and 108 Pershing II missiles in five European countries, starting in December.

Each of the 572 would have a single warhead.

The only way the Soviets can halt the initial deployment, a senior administration official said in the briefing before the speech, is to agree to the original zero proposal.

Under the revised U.S. proposal, the Soviets would dismantle some missiles, in a number yet to be specified, and the United States would begin deploying missiles until an equal number is reached. Then both sides would remove missiles until all were eliminated.

Administration officials said the number of missiles permitted by an interim agreement was a matter for negotiation. A limit of 300 warheads for each side essentially would allow the Soviets 100 triple-warhead missiles and the United States 300 single-warhead missiles.

Officials said yesterday they want to keep a mix of Pershing and cruise missiles in any interim deployment, including some missiles in each of the five countries, to maintain NATO cohesion.

Officials also stressed that the limits on Soviet SS20s must be "global." That means Moscow would have to reduce or dismantle not only 243 missiles in the European part of the Soviet Union which have been the center of concern, but also 108 based in Asia about which the Japanese and Chinese have recently raised concern.

This is potentially a major complication in the negotiations.

The Soviets have contended since 1979, when NATO decided on the future deployment, that there already was a balance of power and that no new U.S. missiles were justified.

Washington points out that Moscow has added almost 300 new missiles since then, though it also has dismantled some older ones.

The Soviets also want 162 British and French missiles, mostly based on submarines, counted in any agreement. The allies say no because those missiles are not under NATO control and are meant to defend only France and Britain.

But the British plan to replace their current single-warhead Polaris missiles with eight-warhead Tridents in the 1990s, adding fuel to Soviet arguments.

Reagan later flew to California, where he is scheduled to address the Los Angeles World Affairs Council today on the same subject.

On Capitol Hill, the president's statement was generally applauded.

"His proposal is sound, fair, and based on close consultation with our allies," said Senate Foreign Relations Committee Chairman Charles H. Percy (R-Ill.).

Sen. Larry Pressler (R-S.D.), chairman of its subcommittee on arms control, called the proposal "the most significant breakthrough...in over two years," and said Reagan's "real achievement may very well be an arms control agreement."

Sen. Joseph R. Biden Jr. (D-Del.), a member of the Senate Foreign Relations and Intelligence committees. said Reagan "should be complimented for recognizing the significance of the European reaction."

Rep. Edward J. Markey (D-Mass.), sponsor of a nuclear freeze resolution expected to be passed by the House, said the freeze movement deserves credit for putting pressure "on the White House to get more serious about arms control."

Former vice president Walter F. Mondale, a candidate for next year's Democratic presidential nomination, said he hoped the Reagan proposal is a sign of "long overdue willingness to get serious about arms control."

The Union of Concerned Scientists welcomed "what appears to be the willingness...to compromise," and expressed hope that the proposal "is not just another attempt to weaken popular support for the upcoming freeze vote in the House."