The Kennedy Center Concert Hall was awash in a sea of black ties and long gowns Saturday night as 1,500 guests gathered to commemorate the 36th anniversary of the United Nations and honor the Organization of American States.

The big applause of the evening went to Secretary of State Alexander M. Haig Jr., who strolled on stage with one hand in pocket just before the concert began.

"I feel like my career is on the rise," he said. "Two weeks ago I was with Bob Hope and now I'm before a full house at the Kennedy Center."

Keeping the crowd of congressmen, ambassadors and industry leaders chuckling, Haig said, "Politicians think they have it hard because a politician has to get along with people. But, a statesman has to get along with politicans."

And politicans by the score filled the Concert Hall:

Former ambassador to Great Britain Elliot Richardson; Jeane J. Kirkpatrick, U.S. ambassador to the United Nations; Alejandro Orfila, secretary general of the OAS; Carmen Romano de Lopez Portillo, first lady of Mexico; Samuel R. Pierce, secretary of housing and urban development; and Edwin Meese III, presidential counselor.

And politicians, it seems, sometimes have to get along with corporate chairmen, of which there was a sure score. Among them: Rockwell International's Robert Anderson; Charles Brown, chairman of American Telephone and Telegraph;and Paul Henson, chairman of United Telecommunications Inc.

After the performance and a rousing encore by the Mexico City Philharmonic and conductor Fernando Lozano, the chauffeured limousines, lined up like markings of a perforated line in front of the Concert Hall, sped the crowd to the International Ball Room at the Washington Hilton. The sounds of "Leroy Brown" and "Sentimental Journey" from the band provided a lively greeting as couples beelined it to the spacious dance floor.

"Now this is music I can relate to," Meese said, in between dances.

At the 148 tables decorated with small grinning jack-o'-lanterns, fall colors and champagne bottles, few seats went unoccupied. Red-jacketed waiters and waitresses scurried amid the chatter and carnation-crowned hostesses to keep plates filled with scallops or Caesar salad and glasses brimming with red and white wines.

Talk did turn to business for brief moments throughout the evening. When asked about the voting for secretary general of the United Nations, Richardson made his prediction.

"Waldheim will, in the end, be reelected."

As the pineapple halves filled with sherbet and topped with coconut appeared for dessert, the dance floor was filled to capacity.

"How're you enjoying the party?" Orfila and a guest were asked while coming off the dance floor.

"Alejandro is a just a wonderful dancer; he's just a fantastic dancer," his blond partner said.

Orfila's answer: a grin, as he made his way back to his table.