Soviet President Leonid Brezhnev yesterday sharply attacked the West for its action in Africa and charged that U.S. claims of Soviet and Cuban involvement in Zaire were "falsifications."

In his first major speech since the furor that surrounded the recent invasion of Zaire's Shaba Province, Brezhnev also attacked NATO countries for making "new warlike preparations" at their Washington summit while talking about disarmament.

His speech in Czechoslovakia underscored the severe strains in East-West relations that have become apparent in Washington in recent days.

The Soviet leader attributed this strain to unnamed "political circles" in the West which, he said, "are openly trying to mar to process of detente - not only in Europe - and to return if not to the Cold War then at least to a chilly war."

"This direction is taken through such actions as the bloody intervention of NATO member states in Zaire," Brezhnev said.

He did not mention Zbigniew Brzezinski by name, but for the second day in a row the Soviet Communist Party newspaper Pravda attacked President Carter's national security adviser as an "enemy of detente" who viewed international relations through "a prism of anti-Sovietism."

The sharp criticism of Brzezinski was prompted by his charge that the Soviet Union shared responsibility with Cuba for the rebel raid into Shaba Province.

Referring to the combined operation by French and Belgian paratroopers to rescue their nationals and other Europeans in southern Zaire, Brezhnev said:

"NATO circles are trying to divert attention from the cynical character of this intervention by masking it in a propaganda campaign about supposed Soviet and at other times Cuban participation in these events."

Brezhnev's speech was televised and broadcast throughout Eastern Europe, but the transmission was inexplicably cut off midway through the 30-minute address. Soviet officials blamed "technical difficulties" for the interruption.

This caused immediate speculation here that a dissident Czech may have pulled the plug on transmission equipment, but there was no evidence to support this idea.

The Czechoslovakian police have already taken extensive precautionary measures to prevent possible demonstrations during Brezhnev's four-day visit here. Dissident sources reported that at least 25 human rights activists have been picked up at their homes.

Among the detained was the playwright Vaclav Havel, one o f the founders of the human rights group, Charter 77. Havel, the country's best known dramatist, was given a 14-month suspended sentence earlier this year for allegedly smuggling antistate material abroad.

Brezhnev, 71, addressed Czechosiovak Communist leaders at a rally in Prague's historic Hradcany Castle. In his public appearances, which have been kept to a minimum, he appeared basically fit but seemed to move with some difficulty. Some diplomatic observers suggested that Brezhnve has become visibly more tired as the visit has progressed.

Speaking about disarmament, Brezhnev said that policies of NATO countries are "full of contradictions."

"Here is a clear illustration," he continued. "The summit session of the NATO council is now being held in Washington. Some of its participants, on the way to the meeting or on the way back home, stop over in New York (to) visit the special session of the United Nations and say high sounding words about disarmament. While at The NATO session, in the same breath, they talk about plans for new military preparations for many years ahead."

Brezhnev and Czechoslovak President Gustav Husak both dwelt at length on the history of cordial relations between the Soviet Union and Czechoslovakia. Husak warmly thanked the Soviet Union for the 1968 invasion that ended Alexander Dubcek's attempt to liberalize the government.

Husak, who replaced Dubcek as party leader after the Soviet invasion, was hailed by Brezhnev as an "outstanding son of the Czechoslovak nation" who has followed a "correct policy" since taking over.

"In discussing the European situation, Brezhnev said the "durable peace in Europe is undoubtedly one of the dicisive conditions for preventing a new world war." He said the Helsinki conference in 1975 had created opportunities for better East-West relations.

But, he said, "the fact is that many useful initiatives of "Warsaw Pact countries" do not meet with a desired response." He added that Moscow was ready to negotiate disarmament measures with the West.

"There does not exist any type of weapon that the Soviet Union would not be willing to limit and ban on the basis of mutual agreement with other states," Brezhnev said.

But this would have to be done, he said, "without damaging the security of anybody and under conditions of complete mutual agreement between those states which own the arms."