BREZHNEV CHARGES U.S. IS THREATENING NUCLEAR CONFLICT

Leonid I. Brezhnev told a gathering of Soviet military leaders today that the United States was threatening ''to push the world into the flames of a nuclear war.'' He also said the Soviet Union would do ''everything in our power'' to normalize relations with China.

In a speech to some 500 generals and Defense Ministry officials summoned Excerpts from speech, page A7. to the Kremlin, the Soviet leader accused the United States of pursuing a foreign policy of ''adventurism, rudeness and undisguised egoism.''

Perhaps by coincidence, Mr. Brezhnev spoke on the eve of the 20th anniversary of the day in 1962 when Nikita S. Khrushchev bowed to President John F. Kennedy's demands for the dismantling of Soviet missiles in Cuba. Mr. Khrushchev's retreat left Soviet generals vowing never again to be caught short of military strength in a confrontation with the United States. Brezhnev Seeks to Assure Army

Most of Mr. Brezhnev's speech dealt with assurances that the Soviet leadership recognized the need for military strength and was prepared to commit the necessary resources.

He said that, while the Soviet Union continued to stand for detente, it recognized that ''not only words'' but military strength were needed to deal with what he called the American threat. Accordingly, he pledged support for a drive to increase the combatreadiness of the Soviet armed forces and for an upgrading of military technology.

His speech also marked an explicit Soviet use of the ''China card.'' For months Soviet leaders have been calling for an end to the deep-seated ideological and territorial disputes that have divided Moscow and Peking for two decades. After a break of three years, the two sides resumed talks in Peking earlier this month and agreed to continue them in the two capitals. Connection With U.S. Policy

Previously, the Soviet Union had called for improved relations with China as a goal in itself. Today, Mr. Brezhnev made an explicit connection with the strained Soviet-American relationship. He said United States policy had made Soviet relations with other nations ''very important,'' and he mentioned specifically China.

In a passage that suggested that the Soviet Union was not discouraged by the first phase of the renewed talks, he noted that the Chinese leaders, too, had expressed interest in closer ties.

''Of no small importance are rela-tions with China,'' he said. ''We sincerely want a normalization of relations with that country and are doing everything in our power toward this end. In Peking, they also say now that normalization is desirable.

''No radical changes in the foreign policy of the People's Republic of China are to be seen so far. But the new things which appear must not be ignored by us.''

Both Chinese and Soviet officials said after the Peking talks that they expected no early resolution of the differences between the two nations.

The unusual nature of the Kremlin gathering, and Mr. Brezhnev's assurances of backing for the armed forces, suggested that the party leadership was seeking to ease concern in the military that responses to the United States had not been tough enough.

This interpretation was strengthened by a new emphasis in Mr. Brezhnev's remarks. In previous speeches during the 21 months of the Reagan Administration, the main theme was generally the importance of detente and of restoring an equilibrium through arms negotiations, trade and other contacts.

This time there was only a brief passage about detente and no mention of the two sets of nuclear arms reduction talks under way in Geneva, on strategic, or long-range, weapons, and on medium-range weapons in Europe.

Instead, there was a strong hint in Mr. Brezhnev's remarks that a Soviet freeze on the deployment of medium-range missiles might be abandoned soon if American preparations for the deployment of equivalent missiles in Europe were to continue.

Western diplomats said that, while the change in tone owed something to the fact that Mr. Brezhnev was addressing a military audience, it also implied a stiffening of the Soviet posture.

''The masses of people on all continents,'' Mr. Brezhnev said, ''angrily protest against Washington's aggressive policy, which is threatening to push the world into the flames of a nuclear war. The adventurism, rudeness and undisguised egoism of this policy arouse growing indignation in many countries, including those allied with the U.S.A.''

The occasion had implications for Soviet domestic politics. Diplomats could not recall a previous occasion when a Soviet leader felt obliged to offer such public assurances to the military. Moreover, the speech contained a passage in which Mr. Brezhnev, who is 75 years old and in failing health, appeared to be trying to scotch rumors that he was no longer in command.

In the presence of five other members of the ruling Politburo - including the two men favored eventually to succeed him, Yuri V. Andropov and Konstantin U. Chernenko - Mr. Brezhnev noted that Defense Minister Dmitri F. Ustinov, ''constantly reports'' to him about military matters. His words slurred, he added:

''I also constantly handle matters of consolidating the army and navy in the performance of my official duty, so to say, and know about the state of affairs.''

Some of the solutions to economic problems, including increased investment in agriculture, appear to have created anxieties in the military about a budget squeeze. But Mr. Brezhnev, who has gained a reputation in 18 years as a Soviet leader for giving the armed forces almost everything they want, promised that they would be getting even more in the future.

''We are equipping the armed forces with the most advanced weapons and military hardware,'' he said. ''The party's Central Committee is taking measures to meet all your needs.''

It was at this point that he indicated concern that the Soviet forces were falling behind in military technology. ''Competition in military technology has sharply intensified, often acquiring a fundamentally new character,'' he said. ''A lag in that competition is inadmissible. We expect our scientists, designers, engineers and technicians to do everything possible to resolve successfully all tasks connected with this.''