The antiwar movement came together again today for a victory celebration - another, if not last hurrah.

The men and women who marched to ally opposition to the Vietnam war crowded into a Manhattan theater to shake hands with and welcome the Vietnamese delegation to the United Nations.

Today, he protesters carrying placards outside were Vietnamese - about 250 exiles singing the songs and waving the flags of their vanished nation, South Vietnam.

Some of the roughly 2,500 Americans making their way into the theater tried to sing down the Vietnamese. None appeared interested in the placards proclaiming that "Vietnam traples upon human rights."

Inside and outside the theater, one message was the same, however. The crowd was told by the protesters standing in the rain and by the speakers on the stage that they all are friends of the Vietnamese people. And in both places the talk was of freedom. The crowd inside liked the message better.

"Isn't it good to be here?" asked Cora Weiss, the event's organizer and a longtime opponent of America's Vietnam policy. In the crowded lobby, guest after guest agreed. "Smile, this is a great day," one woman told a friend. "Isn't this great?" people said upon meeting.

And they stood, applauded and whistled for minutes when the Vietnamese delegation entered the theater after shaking hands for an hour on a receiving line in the lobby. Vietnam was formally admitted to the United Nations last week.

"The war is over," as posters in the lobby noted which leaves the antiwar movement without its cause. But many of its leaders deny that the movement will die away, and would object to labeling today's rally a last hurrah.

David Dellinger, who has marched in unpopular causes since World War II, made it clear that he sees a new wrong for the movement to right. He cannot understand. Dellinger told the crowd, how anyone who favored the independence and sovereignty of Vietnam would not favor the independence of Puerto Rico. Dellinger's reference to "the war against the Puerto Rican people" was cheered.

Cora Weiss pledged that the organization she heads. Friendshipment, would launch a new campaign to persuade President Carter and Congress to approve U.S. aid for Vietnam. But, while looking to the future, her speech also contained a nostalgic call of the antiwar movement's honor roll.

As she called out each, name - Norman Morrison who set himself on fire outside the Pentagon, the Gls of Ft. Hood who first said "I won't go," and many more - the audience applauded. The lougest applause was for the four students shot dead at Kent State.

The Vietnamese, Weiss said, will never forget their war for independence, but now may not remember the role some of them played in ending U.S. involvement in Vietnam.

Ngo Dien, the deputy foreign minister for press and information, replied on behalf of the Hanoi delegation. He said the late President Ho Chi Minh had spoken of taking a trip abroad after the final victory in order to thank people around the world who had helped his cause. Ngo Dien said Ho would have been delighted with today's welcoming party.

"Long live the friendship of the Vietnamese and American people," he said in conclusion, and the audience stood and clapped as he clasped his hands over his head.

The mood was joyful, but not markedly forgiving. There was warm applause for Ho Chi Minh, but only scattered handclaps when Weiss and the United States is "a great naiton." That was not what the people came to hear. This was a victory party and the United States lost the way.