President Reagan today used the forum of a U.N. disarmament conference to accuse the Soviet Union of tyranny, aggression, atrocities and "ruthless repression" while simultaneously urging Soviet acceptance of what he called a U.S. "agenda for peace."

In the most toughly worded address ever made to the United Nations by an American president, Reagan repeatedly denounced Soviet conduct since World War II and questioned the sincerity of Soviet arms control initiatives and responses.

While Reagan made no direct reference to Soviet Foreign Minister Andrei F. Gromyko's proposal earlier this week renouncing first use of nuclear weapons by the Soviet Union, the president strongly indicated that he regarded this promise as meaningless. He also said that arms control agreements negotiated with the Soviets would be worthless unless they could be verified reliably.

"Simply collecting agreements will not bring peace," Reagan said. "Agreements genuinely reinforce peace only when they are kept. Otherwise we are building a paper castle that will be blown away by the winds of war. Let me repeat, we need deeds, not words, to convince us of Soviet sincerity, should they choose to join us on this path."

The Soviet delegation and representatives of several other communist countries greeted these remarks with silence and did not applaud when the president finished. Otherwise, Reagan received polite rather than enthusiastic applause from most of the delegates, but the General Assembly chambers, half empty when Gromyko spoke, were nearly filled for the president's speech. Partial text of address on Page 12

After Reagan left many of the delegates clustered around the podium to examine the TelePrompTer he had used. This also happened last week in the Palace of Westminster after Reagan addressed members of the British Parliament.

Much of what the president had to say today was in that London speech or other remarks he made during his 10-day trip to Europe, which concluded last Friday. But the tone and focus of his speech today was as overtly anti-Soviet as any speech he has given since his days as a circuit-riding conservative spokesman for the Barry Goldwater presidential candidacy of 1964.

Reverting to the metaphors and accusations of that campaign, Reagan charged the Soviet Union with establishing a "record of tyranny" that began with violation of the Yalta agreements after World War II and led to Soviet domination of Eastern Europe and construction of "a grim, gray monument of repression," as the president described the Berlin Wall.

"It includes the takeovers of Czechoslovakia, Hungary and Afghanistan and the ruthless repression of the proud people of Poland," Reagan said.

"Soviet-sponsored guerrillas and terrorists are at work in Central and South America, in Africa, the Middle East, in the Caribbean and in Europe, violating human rights and unnerving the world with violence. Communist atrocities in Southeast Asia, Afghanistan and elsewhere continue to shock the free world as refugees escape to tell of their horror.

"The decade of so-called detente witnessed the most massive Soviet buildup of military power in history," Reagan continued. "They increased their defense spending by 40 percent while American defense spending actually declined in the same real terms. Soviet aggression and support for violence around the world have eroded the confidence needed for arms negotiations."

Nonetheless, Reagan again proposed a series of initiatives that his administration has made during the past seven months, today wrapped into a four-point proposal to which the president referred as his "agenda for peace."

The proposals, as summarized by Reagan, call for eliminating land-based intermediate-range missiles in Europe, a one-third reduction in strategic ballistic missile warheads, a substantial reduction in NATO and Warsaw Pact ground and air forces and new safeguards to reduce the risk of accidental war.

In addition, Reagan today added a minor new proposal: a call for an international conference on military expenditures, which is part of a U.S. effort aimed at persuading the Soviets to give more accurate and detailed information about their military forces. The Soviets regularly publish such information, but the United States contends that actual Soviet military spending far exceeds the official figures.

Reagan frequently has denounced purported Soviet use of chemical warfare in Afghanistan and supply of toxins--"yellow rain"--in Southeast Asia. Today he called for a formal U.N. investigation of these "horrors," expanding on an appeal that has been made by officials of his administration.

"The Soviet Union and their allies are violating the Geneva Protocol of 1925, related rules of international law and the 1972 Biological Weapons Convention," Reagan said. "There is conclusive evidence that the Soviet government has provided toxins for use in Laos and Kampuchea, and are themselves using chemical weapons against freedom fighters in Afghanistan."

Reagan reviewed with pride the U.S. international record since World War II, saying that U.S. governments had never been the aggressor and had labored diligently for genuine arms control. During the past decade, he said, the United States had exercised "unilateral restraint" while the Soviets "forged ahead and today possess nuclear and conventional forces far in excess of an adequate deterrent capability."

"Soviet oppression is not limited to the countries they invade," Reagan said. "At the very time the Soviet Union is trying to manipulate the peace movement in the West, it is stifling a budding peace movement at home. In Moscow, banners are scuttled, buttons are snatched and demonstrators are arrested when even a few people dare to speak about their fears."

And while Reagan said that peace was his paramount goal, he also expressed his view that peace by itself is not enough.

" . . . Peace would be a terrible hoax if the world were no longer blessed with freedom and respect for human rights," he said.

After his speech, Reagan visited the U.S. mission here, where he was greeted by U.N. Ambassador Jeane J. Kirkpatrick, who sat next to Secretary of State Alexander M. Haig Jr. in the General Assembly chambers during the president's speech.

Later, responding to a luncheon toast from U.N. Secretary General Javier Perez de Cuellar, Reagan praised the "shining accomplishments" of the United Nations. The president, who once proposed reducing the U.S. contribution to the United Nations, said that on balance the organization "has been and can be a force for great good."

"Perhaps now we have a more mature view of the United Nations," Reagan said. "While recognizing its limitations, we don't overlook its real potential and the opportunities--opportunities that for the sake of humanity we cannot afford to waste." Reagan specifically praised the secretary general's efforts to "prevent, contain and resolve the conflicts in the South Atlantic, Lebanon and in Iran and Iraq.

While the tone of the speech was more militantly anti-Soviet than many other recent presidential speeches, the address here today appeared to be part of a continuing effort by the administration to keep the Soviets on the defensive.

The approach has been consistently dualistic. On the one hand, Reagan and other administration spokesmen are calling attention bluntly to what they regard as Soviet misdeeds. On the other, they continue in every speech--as Reagan did today--to say that the United States is genuinely interested in negotiating arms reductions with the Soviets.