In the presummit report on Soviet violations of arms-control agreements that accompanied his now-controversial letter to President Reagan, Defense Secretary Caspar W. Weinberger argued that "the key to improved U.S.-Soviet relations is a vigorous response by us to Soviet treaty violations."

Weinberger warned the president that "current and future Soviet violations of arms-control agreements pose real risks to our security and to the process of arms control itself." This threat, he said, could only be overcome with a vigorous U.S. defense program and forceful responses to all perceived Soviet violations.

Acknowledging that his advice to seek better relations with Moscow by being tougher than in the past "may appear paradoxical," Weinberger added:

"It is no more [paradoxical] than the observation that the key to domestic peace is a police force ready to exert itself to preserve the law."

The general contents of Weinberger's findings on Soviet violations were reported last week.

The 11-page, unclassified summary of the detailed study was made available to The Washington Post with the cover letter that has caused a stir. It contains a number of new points, as well as a glimpse of the passion behind Weinberger's views.

They represent the feelings of many administration officials that meetings like this week's in Geneva will not overcome the profound differences between the superpowers.

The cover letter included a warning from Weinberger to Reagan not to agree to continued adherence to provisions of the SALT II arms-control agreement and not to accept limits on research, development and testing of a new strategic defense against incoming missiles. Publication of the letter Saturday led a senior White House official to describe it as an attempt to "sabotage" the summit.

Secretary of State George P. Shultz said yesterday that Reagan will mention past Soviet violations in his conversations with Gorbachev, which are scheduled to begin Tuesday.

In his report, Weinberger disclosed that a new CIA study of the phased-array radar the Soviet Union is building in Siberia "confirms that the Krasnoyarsk radar is not suited for the purposes claimed for it by the Soviets but is indeed an early-warning radar."

The Soviets have claimed that the radar was intended to track objects in space. The 1972 ABM treaty requires that early-warning radars be located on the periphery of each superpower, not in the heart land, as is the facility near Krasnoyarsk.

The defense secretary said the construction of this radar together with "a variety of other violations . . . of the [1972] ABM treaty" represent a systematic pattern suggesting that the Soviets may be preparing a defense against incoming ballistic missiles that "could have a profound impact on our strategic deterrent forces.

"Even a probable territorial defense," Weinberger wrote, "would require us to increase the number of our offensive forces and their ability to penetrate Soviet defenses to assure that our operational plans could be executed."

This is the same reasoning used by many critics of Reagan's Stratetgic Defense Initiative, who argue that if the United States proceeds toward development of a defense, the Soviets will inevitably respond by adding to their offensive forces -- or at least by refusing to reduce them -- to improve their ability to counter the U.S. defense.

Repeatedly in his executive summary, Weinberger argued that "failure to object or respond to violations will invite further violations," as he put it at one point. And he made no effort to hide the strength of his feelings.

For example, Weinberger dismissed the body set up to monitor compliance with past agreements, the Standing Consultative Commission in Geneva, as "a diplomatic carpet under which Soviet violations have been continuously swept, an Orwellian memory-hole into which our concerns have been dumped like yeterday's trash."

Weinberger compared those who close their eyes to Soviet violations to appeasers in the 1930s who allowed Adolf Hitler to rearm Germany. Failure to respond forcefully to Soviet violations now "would signal the kind of uncertainty and political weakness that invites adversaries to put one further to the test" and could "undermine our credibility."

Several times in the document, Weinberger warmly praised Reagan. After reciting what he termed the failures of Presidents Johnson, Nixon, Ford and Carter to "respond seriously to the many Soviet violations that took place during their tenures," Weinberger wrote, "you became the first president in five administrations to find the Soviets in violation" and publicly say so.

He was referring to reports urged on Reagan by Weinberger and his key assistant secretary, Richard N. Perle, accusing the Soviets of violating some provisions of past treaties. Publication of those findings followed sharp battles inside the administration.

Weinberger said a decision to respond effectively to the Soviets "requires great political courage . . . . Indeed, you are the first president to decide to do so, and you can expect considerable controversy over any specific proportional response that you chose to make."

Weinberger is to make specific suggestions for such responses in part two of the report he submitted to Reagan last week. That section will not be completed until after the Geneva summit.

One theme of Weinberger's report is that, as he wrote, "our original assumptions that the Soviets would not violate agreements, because the political repercussions would not be worth any possible gain, have been proved false."

In the two SALT agreements and the ABM treaty, he said, "the Soviets insisted on formulations calculated to excuse subsequent actions of precisely the sort the agreements were understood to curtail. And since the agreements were signed, the Soviets have made prodigious use of the loopholes and ambiguities they argued for."

One such ambiguity involves the encoding of test data radioed to Earth from Soviet rockets and warheads during flight tests, known as "telemetry."

The United States had learned a great deal about Soviet weapons by monitoring this data in the past. The SALT II treaty, never ratified, but which both superpowers have pledged not to "undercut," contains a provision banning encryption of telemetry if it "impedes verification" of the treaty.

Weinberger's report accused the Soviets of heavily encrypting data from tests.

"In some cases it is now nearly total," he wrote, having "spread like a range fire" since SALT II was signed in 1979. "Unless reversed," Weinberger wrote, this Soviet encryption "is certain to diminish still further our ability to monitor Soviet activities and to verify their compliance with treaty obligations."

In an aside, Weinberger suggested that the U.S. effort to win restrictions on encryption in the SALT II negotiations "almost certainly alerted Moscow to the importance of telemetry as a source of intelligence about Soviet military programs."

"The Soviets seldom denied us missile test data before we proposed that they undertake not to do so," Weinberger wrote.

On the other hand, Weinberger's report asserted confidently that the United States has been able to determine that a new Soviet rocket, the SS25, is a violation of the SALT II provision limiting each superpower to one "new type" of intercontinental rocket. Moscow earlier declared that their one new type would be the bigger, multiwarhead SS24 rocket, similar to the U.S. MX. The Soviets have called the SS25 a modification of the older SS13.

According to Weinberger, the United States has "convincing evidence" that the SS25 exceeds permissible modifications of older models considerably more than SALT II permits, "despite massive encryption of data during the SS25 flight test program."

Weinberger indicated the United States has been able to measure the rocket's weight, length, diameter, payload and other vital characteristics.

Weinberger was contemptuous of existing mechanisms for enforcing compliance with arms control agreements, particularly the Standing Consultative Commission (SCC), in effect calling on Reagan to abandon that body.

He indicated that there may be a dispute within the administration about this, citing "those who believe that the inadequacies of the SCC can be overcome by a redoubled effort."

Weinberger noted that "a constituency has developed around the SCC composed, as is the SCC itself, of Soviets and Americans who believe that violations of agreements must not be permitted to become prominent features of the arms-control dialogue. Only a clear declaration from the president that the SCC has failed offers any prospect that we will find the will and opportunity" to respond effectively.

The Weinberger report -- drafted, officials said, under Perle's direction -- was requested by the president in June, when he decided to dismantle a Poseidon submarine rather than break through the missile limits in the SALT II treaty with the deployment of a new Trident sub. Reagan asked the Pentagon to assess the military implications of alleged Soviet violations and to recommend responses.

Weinberger acknowledged that his report was downbeat but told Reagan, "I hope you will not consider it too negative or too lacking in hope. I have great hopes myself, based on my certain knowledge of how much you want agreements that will reduce arms."