If it weren't for the abundance of "Kennedy "80" buttons, they could have been attending a college reunion.

Early Saturday evening, the conventioneers began to gather in the Chinese room of the Mayflower Hotel. They drifted across the carpeted floor, drinks in hand, meeting old friends, talking politics, exchanging news. On the whole, beards and pipes were predominant, and the shoes were mainly scuffed.

They were there for the 32nd annual convention of the Americans for Democratic Action (ADA), the oldest surviving liberal organization in the country.

Three of ADA's most venerable members stood in the center of the floor conversing in moderated tones. John Kenneth Galbraith towered benevolently over his colleagues. Sen. Daniel Patrick Moynihan, whose views have become unpopular with liberals, and Arthur Schlesinger, Jr., Known as the dean of American liberalism.

A photographer moved in to capture the threesome on film, and Schlesinger, in his red and black striped bowtie, darted quickly aside.I'm not going to stand with that crowd," he said, smiling.The camera flashed on Moynihan and Galbraith in statesmanlike poses.

"They're just as vain as women," clucked Alma Williams-Selleck to no one in particular.

"Who is he?" asked a white-haired woman pointing toward Galbraith. She didn't know who he was. But she could tell he was somebody.

A reporter asked Galbraith why he was a liberal. He answered deliberately and methodically, as though he were speaking into a dictaphone, which is the way he writes his books: "I know that if I oppose regulation there will be an incident at Three Mile Island, engines will fall out of the DC10 and the Chrysler Corporation will ask to be socialized." Galbraith looked up then, with surprised pleasure. "That's pretty good," he said, "I think I'll use that in my speech tonight."

Someone asked Schlesinger when he joined the ADA. He laughed, and a man standing nearby remarked: "That's like asking when the Pope became a Catholic."

Moynihan, asked why he was a liberal, answered: "Because I'm a member of ADA."

At the opposite end of the room, a clutch of delegates was discussing Stuart Eizenstat, the president's assistant for domestic affairs and policy, who had spoken on behalf of Carter the night before, and braved the onslaught of the ADA questioners.

One New Yorker commented that Eizenstat had "handled himself brilliantly."

A blond, middle-aged woman said: "I felt he was almost apologetic, poor man. I felt sorry for him."

"I thought he looked unhappy," another woman said.

Since its founding in 1947, the ADA has staunchly upheld the values of liberalism in the Democratic party. From Joe McCarthy (against) to Gene McCarthy (for) it has fought the liberal fight, often without regard for the political consequences. In presidential politics, opposing seated Democratic presidents for renomination has almost become an ADA tradition, says one member. This year, the ADA delegates say that Carter has failed them and the country. They want Kennedy to be the nominee.

California Rep. Pete Stark took on Eizenstat Friday night, as the draft Kennedy spokesman. "Senator Kennedy couldn't make it so he sent his hairdo," quipped Massachusetts state representative Barney Frank.

The dedicated Kennedy supporters were numerous and euphoric. Allard K. Lowenstein, who was a prime mover in Robert Kennedy's bid for the 1968 Democratic nomination was wearing a "Kennedy '80" button - on the underside of his tie. The overwhelming majority of the delegates voted noisily in favor of creating an "irresistible national mandate" for a Kennedy candidacy.

Eizenstat, as Carter's representative to the ADA, looked pained. He answered hisses with unshakeable tenseness and the loud ho-hums (there were three of them) with infuriated pauses. He tried to take the audience on "a mythical trip" to the land of ideal presidents, listing all the qualities the ADA would want in such a person. At the end he told the delegates that he had just described Jimmy Carter.

They didn't buy it. In their eyes, Carter has sold out to the oil companies and forgotten the poor. As william "Wimpy" Winpisinger, president of the International Association of Machinists, emphatically said: "We no longer look at each other and say: 'Jimmy Who?" We look at each other and say: "Jimmy Hoover."

A cherubic man rose to the podium and looked out earnestly at the audience. David Mixner, a gay rights activist and a former antiwar organizer, was Jerry Brown's emissary to the ADA convention, and a good symbolic touch as well. When Patsy Mink, ADA national president, listed his qualifications, the disbelieving audience became more respectful.

His voice shaking with emotion, Mixner pleaded with the liberal audience "to hear the words of the hungry, to hear the words of the Indians, to hear the words of the migrants." And breathily whispered: I'm here to ask you to listen."

He went on to extol his candidate Jerry Brown. "Never has there been a greater lover of human rights," he said. "This is a serious man." Mixner concluded with a poem from Pablo Neruda, his eyes filling with tears. It was indicative of the audience that at that moment they were more sympathetic to Jerry Brown than before the speech.

But when Mixner concluded his remarks saying that "Jerry Brown deeply believes [his voice quavered here] in the sun as a source of life and as a source of energy," the prosolar audience hissed this bit of California mellow-speak.

"I don't trust Jerry Brown," said Ed Donahue, vice president of the Graphic Arts International Union. "We don't need rhetoric and rock stars," said Rep. Stark to the audience's cheers. "We need results."

In fact, the mood of the convention was so mistrustful of Brown's politics, that even Wimpy, champion of the ABC (Anybody But Carter) sentiment, put Brown at the bottom of his list of options should Kennedy refuse to run.

After going through a list of alternatives to Carter, including McGovern, Udall and Culver, he gestured in him Mixner's direction, grimaced, and said he might even accept Jerry Brown.

The meeting room was packed and sweaty when it came time to vote on the presidential resolution. Delicate snakes of cigarette smoke wafted up toward the chandeliers. And the moment the conventioneers had been waiting for, the vote on the draft Kennedy resolution, had arrived. They were supposed to raise their hands for the count, but when Patsy Mink called for the ayes, they shouted thunderously.

At that moment, listening to the cheers, the faithful were thinking: "How can he say no?" CAPTION: Picture 1, Sen. Daniel Moynihan and John Kenneth Galbraith, by John McDonnell - The Washington Post; Picture 2, Arthur Schlesinger Jr. speaking at the ADA convention, By John McDonnell