UNITED NATIONS, MARCH 2 -- Every major U.S. ally, with the exception of Israel, joined today in supporting a General Assembly resolution that holds Washington in violation of its treaty obligations for enacting legislation that would oust the Palestine Liberation Organization's observer mission at the United Nations.

The sharp slap at the United States came by a vote of 143 to 1, with only Israel opposed and the American delegation refusing to participate in the balloting. There were no abstentions, a rare event at the United Nations, although several absentees, such as El Salvador, were avoiding offense to Washington.

The criticism coincided with the announcement today in Brussels that Secretary of State George P. Shultz would head back to the Middle East to pursue his peace initiative, which involves the seminal issue of who should represent Palestinian interests, and in what forum.

The diplomatic uproar stems from a rider to the Foreign Relations Authorization Act that won broad bipartisan support on Capitol Hill but was opposed by the State Department.

For most U.S. allies, the issue extends beyond Middle East politics to the legal status of all U.N. missions, which are the equivalent of embassies in capitals.

"At stake at this point are the effective functioning of the U.N. and the right of the organization to hear the views of those invited to attend as observers," said Canadian Ambassador Stephen Lewis, speaking on behalf of Australia and New Zealand as well as his own government.

Since the legislation's adoption in December, the State and Justice departments have been wrestling over whether the executive branch should put the law into effect on March 21, as ordered by Congress, or should challenge its legality. Attorney General Edwin Meese III is said to have decided on the former course, but to have withheld announcement of his decision -- and formal notification to the United Nations and the PLO -- until Shultz returns from his Middle East shuttle.

Because of this, the American delegation was able to argue today that the assembly, which reconvened for three days specifically for this issue, was acting prematurely.

"The U.S. government has made no final decision concerning the application or enforcement" of the law, said Herbert Okun, the U.S. deputy ambassador. "Since we regard this resumed session as premature and inappropriate, the U.S. has again chosen not to participate in the vote."

In the view of the United Nations and other governments, however, the action was overdue. The main resolution called on the United States to arbitrate the matter under the dispute settlement procedure specified by a 1947 treaty between the United States and the United Nations. The treaty defines American obligations and the United Nations' right to invite observers to its sessions.

The U.N. resolution also states that application of the law "would be contrary to the international legal obligations" of the host country, the United States.

A companion resolution, adopted by the same majority and without Israeli opposition, asks the World Court at The Hague, the United Nations' judicial arm, to give a nonbinding opinion before March 21 on whether Washington is obliged to resolve the dispute through arbitration.

U.S. officials privately expressed hope that some accommodation could be reached to put aside the politically delicate issue until after the U.S. presidential election. The PLO ouster still has the support of a number of presidential candidates, among them Sens. Bob Dole (R-Kan.) and Paul Simon (D-Ill.) and Rep. Jack Kemp (R-N.Y.).

The American Jewish establishment initially lobbied for the law, but is now split. Organizations such as the American Jewish Congress have backed away from it, but B'nai B'rith and the American-Israel Public Affairs Committee are among those that still support it.

PLO representative Zehdi Terzi said after the vote that his organization would not challenge the law because the dispute is between Washington and the United Nations.