Soviet Foreign Minister Andrei Gromyko today denounced President Reagan's Middle East peace initiative as a maneuver that "focuses everything on the security of Israel alone" and that reflects America's "arrogant and unjustified claims to a leading role in Middle East affairs."

Addressing the U.N. General Assembly, Gromyko sought to shore up the Soviet Union's eroding influence among Arab states, which have charged Moscow with indecisiveness and failure to assist the Palestine Liberation Organization during Israel's invasion of Lebanon.

Gromyko blamed Israel for the killings of Palestinian civilians in Beirut last month and asked, "Could Israel commit aggression and perpetrate genocide against the Palestinians but for its so-called 'strategic consensus' with the United States?"

Charging that both the U.S.-sponsored Camp David peace process and Reagan's initiative are attempts to divide the Arab world through "diktat and enmity," he declared the Soviet Union's support for demands that Israel surrender all occupied Arab territory and agree to creation of an independent Palestinian state.

The central premise of Reagan's plan calls for the Israeli-occupied West Bank and Gaza Strip to be granted eventual self-rule "in association with Jordan." Israel objects to the plan.

Gromyko endorsed the recent Arab League declaration issued at the Fez, Morocco, summit and said that its proposals "go along the same lines as those of the Soviet Union regarding a Middle East settlement."

He said the best way to resolve the Arab-Israeli conflict is to bring all interested parties, including the PLO, together at "an appropriate international conference." Although he did not elaborate, Gromyko appeared to be calling for revival of the dormant Geneva conference on the Middle East, sidetracked in 1978 by the Camp David process.

Gromyko spoke at a time when U.S.-Soviet relations are badly strained.

In the area where the two governments are engaged in major negotiations -- the parallel talks in Geneva on reducing intercontinental and medium-range nuclear weapons -- Gromyko made clear that any hope of progress still lies far in the future.

In June, the Soviets announced that they would not be the first to use nuclear weapons against another country and challenged the United States to make a similar pledge. Today, Gromyko repeated that challenge, accusing the United States of planning for war with the "cold-blooded composure of gravediggers."