The United Nations Security Council voted yesterday to condemn assassination attempts last Monday against three of the West Bank's Arab mayors. It also expressed "deep concern" about Israel's "failure to provide adequate protection" for the civilian population of the occupied territory.

The United States abstained in the 14-to-0 vote that also repeated previous U.N. demands that Israel withdraw from the West Bank, including East Jerusalem. The resolution called on all nations to stop providing Israel with any assistance that could be used to support the Israeli policy of establishing settlements on the West Bank, which is largely populated by Palestinians.

Both in public statements at the United Stations and in background conversations with reporters in Washington, U.S. officials emphasized that the U.S. abstention represented no change in policy.

Their stress on this point underlined the domestic political sensitivity of the abstention, however, following President Carter's reversal in March of a U.S. vote for a Security Council resolution that called for Israeli withdrawal from East Jerusalem.

From London, meanwhile, Washington Post Correspondent Leonard Downie Jr. reported that European diplomats are preparing a resolution for the Common Market that will formally recognize the Palestine Liberation Organization the Palestine Liberation organization as "a representative" of the Palestinians entitled to a place in peace negotiations on the Middle East.

Nablus Mayor Bassam Shaka lost both legs, and Ramallah Mayor Karim Khalaf lost a foot in the bombings on Monday. Mayor Ibrahim Tawil of El Bireh escaped injury from a third bomb, which severely wounded an Israeli police demolitions expert. Isralei investigations have centered on suspicions that the attacks were carried out by Israeli extremists.

The seven-point resolution, introduced by Bahrain on behalf of Arab nations, reaffirmed "the overriding necessity to end the prolonged occupation of Arab territories occupied since 1967, including Jerusalem." The document also called on Israel to compensate the victims of the terror attacks and their families.

U.S. Aambassador Donald F. McHenry said he had abstained because the resolution "contains a number of provisions which we cannot approve and as a whole is incomplete." He did not elaborate.

White House officials said the United States continued to be committed to U.N. Resolution 242 as the basis of any negotiations and stressed that the abstention did not represent any weakening of a U.S. refusal to accept changes in Resolution 242 or the Camp David accords. West European and Arab nations are pushing for a formal declaration of Palestinian rights to self-determination to break the current negotiating deadlock on the West Bank.

A later statement from the U.S. mission at the United Nations deplored the "cowardly attacks" on the mayors but equated them with a Palestinian terrorist attack in Hebron last month that left six Israelis dead. The separate raids were described in the U.S. statement as part of "an accelerating cycle of violence."

The Security Council resolution, the fourth passed on the west Bank issue since March 1, did not mention the Hebron murders. It did call for the "immediate apprehension and prosecution" of the culprits who attacked the Arab mayors.

Voting in favor of the resolution were China, the Soviet Union, Britian, France, Portugal, Norway, Tunisia, East Germany, Niger Zambia, Bangladesh, the Philippines, Mexico and Jamaica.

From London, Washington Post correspondent Downie reported:

European diplomats are recommending that the leaders of the nine nations in the European Community declare at next week's EC summit that the PLO be included in peace negotiations on the Middle East.

The lastest draft of a declaration to be made in Venice names the PLO as the "representative" of one of the "parties" that should become "part of the peace process," according to informed diplomatic sources. Its adoption would be a significant step beyond previous European statements on the right of Palestinians to self-determination.

The draft declaration, drawn up by Common Market representatives this week in Brussels, must be approved by their foreign ministers and heads of government at the summit. Diplomats warn that its final wording is still "in flux" and subject to negotiation in Venice.

There are still disagreements about how far the European leaders should go toward what might be interpreted as recognition of the PLO. France and Italy reportedly are pressing for the strongest possible statement; some smaller Common Market countries are believed to oppose mentioning the PLO by name, and Britain reportedly has sought a compromise similar to the latest draft.

Israel had mounted a diplomatic offensive over the past several months against the growing European move toward recognition of the PLO. It is sending an emissary to several European capitals this weekend seeking to persuade the Europeans to tone down the declaration to be made at the Venice summit.

"There's likely to be a reference to the PLO in the declaration as an important factor that needs to be associated with any attempt to negotiate a lasting peace settlement," said one British source. "But this does not amount to diplomatic recognition of the PLO. Britain does not recognize organizations."

But even that kind of reference to the PLO by the European leaders, especially in a formal declaration that also will codify the European Community's recognition of the right of Palestinians to self-determination and their own independent state, is likely to anger Israel and create problems for President Carter.

European diplomats have agreed to delay a planned attempt to supplement U.N. Security Council Resolution 242 on the Middle East with a resolution recognizing Palestinian self-determination. That decision came after Carter publicly threatened last weekend to block a move with the U.S. veto.

Carter's position is that a move alienating the Israelis will ruin U.S. efforts to revive the stalled negotiations between Israel and Egypt on autonomy for Palestinians in Israeli-occupied territory in Gaza and the West Bank of the Jordan River. Carter also has to worry about Jewish voters who turned out against him in the primaries.

European diplomats insist that they do not want to "cut across" the U.S.-sponsored negotiations between Egypt and Israel. But because they believe these talks are going nowhere while the situation in the Middle East appears to be deteriorating, they want to have ready an alternative European initiative.

So they are proposing that EC leaders give the green light in Venice to diplomatic consultations preparing for the introduction of a new U.N. resolution, perhaps after the November U.S. election.

They also want the European leaders to explore dialogue between the EC and the Arab League, of which the PLO is a member. The dialogue broke off after Egypt joined in the Camp David peace negotiations and was thrown out to the Arab League.

This would disturb the Israeli government. It strongly opposes contacts with the PLO, which it regards a "terrorist organization." The United States generally has adhered to this shunning of the PLO, as many European countries did until recently.

But the Europeans have been under strong pressure from oil-producing Arab nations in the Middle East, as well as relatively poor Jordan, to take a diplomatic role in the Middle East and recognize the necessity of dealing with the PLO if a comprehensive peace is to be achieved. Both British Foreign Secretary Lord Carrington and French President Valery Giscard d'Estaining came back from visits this year to the Middle East Apparently convinced of the logic of this argument.