Caspar Weinberger reflected in the Concert Hall presidential box for a moment. "Oh, I don't know if I can make any major pronouncements on its significance tonight."

The occasion was Saturday night's 25th annual U.N. Concert and Dinner, a $250-a-head fundraiser for the United Nations Association of America that commemorated the 40th anniversary of the United Nations and the World Bank. The event also honored former U.S. representatives to the U.N. and other nations' ambassadors to the United States and the Organization of American States. The festivities were launched by the National Symphony Orchestra's rendition of Beethoven's Symphony No. 4 and Shostakovich's Symphony No. 5 at the Kennedy Center Concert Hall, led by NSO conductor Mstislav Rostropovich.

Weinberger thought again. "It's important," he said of the United Nations. "Keep trying, keep talking. Keep trying."

Elliot Richardson, chairman of UNA-USA, was more forthcoming. The U.N.'s purpose, he said, "is to help develop better approaches to problems that cannot be solved by one or few countries alone . . . But the big development that has undercut this is the deep rift between the Soviet Union and the U.S. . . .

"The U.N. is one of those things where you can think of it in terms of whether the glass is half full or half empty."

Richardson seemed of the full-glass point of view, as he all but jitterbugged -- along with ambassadors and others -- to an orchestral "Rock Around the Clock" medley performed by Lester Lanin and his orchestra at the Washington Hilton dinner following the concert.

And as for attendance on the part of former American U.N. representatives, the glass was definitely half empty -- with no apparent sign of U.N. American alumni Vice President Bush, Jeane Kirkpatrick, Daniel Patrick Moynihan, John Scali -- or cohosts of the evening, Secretary of State George Shultz and his wife Helena. Soviet Ambassador Anatoliy Dobrynin was also absent. But there were many Washington and OAS ambassadors and U.N. associates clearly out to celebrate the occasion.

Uncharacteristically for U.N.-related functions, there were no speeches, just this toast from U.N. Concert and Dinner chairman David S. Lewis, chief executive of General Dynamics Corp., just before the dinner: "Ladies and gentlemen, peace, freedom and justice throughout the world."

Much more characteristic were the dinner conversations that concentrated on East-West tensions, a subject particularly apropos on the eve of the Geneva talks between the United States and the Soviet Union, as well as a near half century of international relations.

"We were looking forward to the proposals," said East Germany's Ambassador Gerhard Herder about President Reagan's speech at the United Nations last week. "But nothing was said. There was a general feeling among my associates that his statement was not to the point . . ."

"The U.N. is the showroom of East and West relations," said Spanish Ambassador to the OAS Alberto Aza. "Relations should be conducted through other scenarios, other channels . . . The international community has failed to organize itself."

"It is exactly because of East-West differences that the U.N. should be used more," said Zdzislaw Ludwiczak, charge' d'affaires at the Polish Embassy.

"We regard U.N. as a safeguard for world peace," said Han Xu, Washington ambassador from China. He spoke hopefully of the Geneva talks, but with disappointment about Soviet-Sino progress. "There are several obstacles. The Soviets' support of Kampuchea, its occupation of Afghanistan and the deployment of Soviet forces along the Sino-U.S.S.R. border."

But there were other subjects to celebrate: the World Bank Group (which will approve some $16 billion in development projects this year, said president A.W. Clausen), the success of the specialized United Nations groups, such as World Health Organization, the Rome-based World Food Program, and other economic and social development agencies, not to mention the U.N. Association itself, which -- said Richardson -- has more than 90 branches throughout the United States, and the OAS, now edging toward its own 40-year anniversary.