The celebration of the United Nations' 40th birthday was marred today when its 159 members were unable to reach agreement on what was to have been the day's centerpiece -- a declaration listing U.N. accomplishments and objectives.

The sticking point, U.S. officials said, was an Arab demand that the declaration contain a call for "the right of self-determination of the Palestinian people," and a phrase implying the objective of having Israel withdraw from all occupied territories.

"It was an attempt at a point-scoring exercise," said U.S. representative Harvey Feldman, "in which one group sought to substitute its national positions for a declaration of principles that would embody the noblest aspirations of mankind and the hopes of the U.N. as a whole."

The United States refused to accept the Arab paragraph, and this prevented the unanimous consent necessary for the adoption of the full text by the General Assembly.

A West European diplomat called the dispute an "unfortunate symbol" of the futility the organization has long experienced. "After the rhetoric of the past week," she said, "here we are, back to the realities, to the real United Nations."

The deadlock solidified at the last minute as the assembly hall was packed with dignitaries, including Vice President Bush, attending the climactic ceremony of the United Nations' week-long celebration.

They heard speeches by Assembly President Jaime de Pinies of Spain and Secretary General Javier Perez de Cuellar, who said, with unintended irony:

"The observance of this anniversary has meaning not so much as a symbol but as an opportunity. The occasion has set the stage to make a fresh beginning and try to overcome current stalemates on major issues."

As he spoke, however, the committee that had spent a year drafting the declaration to be adopted as the assembly's final ceremonial act was in a basement conference room in the throes of the impasse.

Finally, committee chairman Paul Lusaka of Zambia emerged from the closed session and told reporters there would be no declaration.

U.S. officials explained their stand later by saying that if they had accepted the paragraph proposed by Syria and supported by other Arab nations, "it would have reversed American Middle East policy established over the past 20 years."

The Americans said compromise had been reached on nine other controversial sections last night and this morning.

The final events of the anniversary were to be a dinner given by the secretary general for 12 presidents, five vice presidents, one crown prince (Albert of Monaco) and 15 prime ministers, and a U.N. Day concert by the NHK Symphony Orchestra of Japan.

Earlier today, the leaders of the five major powers and India and New Zealand addressed the assembly, bringing to 120 the total number of speeches honoring the event.

British Prime Minister Margaret Thatcher cited new areas in which U.N. involvement is required -- such as coordinating the African famine, ending the global drug trade and acting with more resolve against international terrorism.

She warned that U.N. resolutions couched in "deliberate ambiguity," while they may produce majorities, will not produce solutions. She added that the United Nations is limited in its capacity to "the power of persuasion, not coercion. The U.N. cannot and should not try to dictate detailed solutions to countries involved in disputes."

French Foreign Minister Roland Dumas, however, said that the United Nations, "far from being a mere onlooker, must participate actively in the solution of regional conflicts," which he attributed to "East-West rivalry."

Indian Prime Minister Rajiv Gandhi urged a larger role for multilateral forums in dealing with an "economic crisis of unprecedented gravity." He said the "consensus on development which was painstakingly built in the decades after the Second World War has broken down today" and "must be rebuilt."

Perez de Cuellar summed up the conclave by cautioning that none of the many problems imperiling human peace and advancement "can be removed or overcome by the efforts of any one government alone. All underline the need to strengthen that structure of international cooperation which we call the United Nations."