he Soviet Union bitterly denounced President Reagan's Middle East initiative today and said that "a true settlement" in the region was possible only after Israel abandons all occupied territories and the Palestinians gain the right to establish an independent state.

The authoritative rejoinder to Reagan's speech Wednesday came as an Arab summit meeting opened in Morocco and clearly suggested an effort at persuading Arab leaders to reject the American initiative.

Western diplomatic observers were surprised by the harsh tone of the long, detailed editorial in the Communist Party newspaper Pravda. The government news agency Tass reprinted it in full.

These observers suggested the Soviets may be concerned that the Reagan plan received a guarded welcome in some Arab countries. The Soviets also may be aiming to strengthen the position at the summit of the hard-line Arab leaders who have consistently rejected any compromises with the Israelis, in the view of these sources.

The editorial also appeared to suggest Soviet frustrations over their inability to influence events in the Middle East following the defeat of the Syrians and Palestinians in Lebanon. The two are Moscow's key allies in the region.

In attacking Washington as a "self-appointed mediator" trying to "arrogate to itself the right to determine" the political map of the Middle East, Pravda argued that the recent bloodshed in Lebanon was an act of "American-Israeli collusion."

Having driven out the Palestine Liberation Organization from Beirut, the editorial said, the Americans have now contrived a feud with Israel in an attempt to win the trust of the Arabs.

"The stage-managed 'differences' between the United States and Israel after Tel Aviv's rejection of the Reagan initiative are aimed only at distracting the world and Arab public from the continuing American-Israeli aggression," it added.

Pravda rejected Reagan's plan for self-government for the Palestinians in the West Bank and Gaza Strip in some form of association with Jordan.

"As a matter of fact," it said, "Washington's so-called new proposals program a further worsening of relations between various peoples and new, bloody conflicts. They are aimed at consolidating American-Israeli rule."

The Soviet Union, it said, "believes that a true Middle East settlement is possible only on the basis of withdrawal of the Israeli aggressors from all the occupied territories, with due regard for the vital interests of the Palestinian people, recognition of their right to self-determination up to the creation of their sovereign, independent state."

Washington's objective, the editorial said, is to "find ways for leaving the Palestinians eternally under wardship, homeless, to doom them to eternal wandering."

In advancing his proposals, Pravda said, Reagan saw a way to revive the Camp David process, "which remains the foundation of the American policy."

Israel's outright rejection of the proposals, the editorial said, was a prearranged move that suited U.S. interests.

It called the move "a crude game of the aggressor and its assistant" -- and said it allowed Reagan to gain some credibility in the Arab world.

Behind this elaborate stratagem, it continued, is Washington's aim to dominate the Arab world. This is justified by the claim that the Middle East "is for the United States a zone of vital interest."

Pravda added, "One cannot imagine a just and lasting peace when aggressive objectives rather than peaceful ideas of cooperation" are the basis of Reagan's proposals.