Sen. Edward M. Kennedy (D-Mass.) arrived today with a burst of public bravado but the growing private recognition that he probably cannot win the presidential nomination at the Democratic National Convention here next week.

In an energetic, upbeat speech before several thousand supporters at a noontime "Welcome Ted" rally in mid-Manhattan, Kennedy predicted victory. But his advisers said they still lack the votes to win the "open" convention rules fight when the convention begins Monday. Without an open rule, Kennedy's nomination is probably impossible.

His staff is drafting a "contingency" speech for possible Tuesday delivery conceding the nomination, though aides say stoutly that they are also drafting a contingency acceptance speech in the event that Kennedy wins.

If the Kennedy side loses the rules vote, campaign aides said, Kennedy might use his speech before the full convention Tuesday to concede that his presidential candidacy has failed. One adviser said he might say, in effect, "My candidacy is over, but my cause goes on."

Despite his repeated losses in the primaries, Kennedy never talked about the possibility of losing. "My father always said," he would observe, "that if you start talking about coming in second, you'll never come in first." "

An incident in his Senate office in Washington earlier this week also suggests that the candidate, like his campaign staff, is growing reconciled to impending defeat.

Kennedy's staff was preparing him for a television interview with journalist Bill Moyers. An aide, firing off questions that Moyers might ask, tried this one: "Senator, what have you learned in this campaign?"

Kennedy thought for a moment and then replied that he had learned how to lose. He said that he came from a family that was accustomed to winning, and that he had never lost an election before the 1980 campaign. But now, he said, he had discovered that losing is not the end of the world.

There was no such talk today, though, when Kennedy stood on an outdoor platform at the Waldorf-Astoria Hotel and told a cheering, chanting crowd that he would win the nomination.

Kennedy's liberal "cause" is reflected in a series of minority reports his backers will try to add to the party's platform at the convention Tuesday. Today, President Carter's campaign manager predicted that the Kennedy forces might win convention floor fights on some of the platform issues.

Kennedy victories in the platform debate might be a prelude to his support of the Carter-Mondale ticket during the fall campaign. In recent weeks, Kennedy has repeatedly ducked questions about his possible support of Carter, but he has said he will support any Democratic nominee who supports a platform that "is true to the traditional principles of the Democratic Party."

Kennedy's confident rhetoric in speeches and interviews here today was of a piece with the things he has been saying throughout his unsuccessful campaign for the presidency.

Today, Aaron Copland's "Fanfare for the Common Man" blared forth from giant speakers on the street, and the Kennedy supporters waved red posters that said "Keep It Open" as Kennedy and his wife, Joan, were introduced by Rep. Shirley Chisholm (D-N.Y.).

Reminding the crowd of his upset win in the New York primary in March, Kennedy said, "You sent the nation a clear message last spring. And now that message has come to the screen: the Empire State Strikes Back."

Whatever his private thoughts about a united party, Kennedy in public was as harsh on Carter as he ever was during the primary campaigns.

"Do you want four more years of double-digit inflation?" he shouted, and when the crowd roared back its "No!" he went on through the litany, "Do you want four more years of unemployment? . . . Four more years would be four years too many."

Kennedy also warned that, "We cannot afford a candidate who will be quoting Herbert Hoover in the fall."

Kennedy's speech Tuesday will come during the convention debate on the 1980 platform resolutions, including several planks that the Carter officials concede Kennedy will win.

"I think we're going to lose a number of those issues on the platform," campaign manager Robert S. Strauss said in a news conference today. He specifically cited the minority report concerning jobs. This is Minority Report 9, which states that providing a job for every American who wants to work is the top priority of the Democratic Party.

The president believes that other factors, such as reducing inflation, are just as important, Strauss said. He called the Kennedy-backed minority position "simplistic." But, predicting defeat for the Carter position on the issue, he added: "We're going to look like we're in a black hat on this one." i

Strauss also conceded the probability of a Carter defeat and a Kennedy victory on economic policy and other platform issues, but it was clear that the Carter forces now feel the defeat will not be a political setback, and could prove enough of a political enticement to the Kennedy forces to encourage them to support Carter in the fall if he is nominated, as expected.

Strauss said he was confident that Kennedy will reconcile his differences and support the Carter-Mondale ticket in the fall.

And Strauss said he believed the president will begin to close the lead now held by Republican nominee Ronald Reagan after what he said will be a show of Democratic unity at the close of the convention.

"My judgment is those polls will begin to close as we come out of this convention," Strauss said. "The president has serious political problems, we all know that. But the president's problems are less serious than those of Ronald Reagan.

Strauss said he was confident that the Carter forces would repel the Kennedy-led effort to defeat a convention rule that would require delegates to vote for the candidate they supported during their state primary or caucus.

Strauss said that under his campaign's "worst-case scenario" the Carter forces still had more than 300 votes more than the forces of Kennedy and others who are advocating an open convention.

Strauss said that the Carter staff had spent a couple of days talking to Carter delegates to see if, as a gesture of conciliation, they favored having the president publicly release his delegates from their binding pledge to vote for him. Such a plan had been proposed by some Carter supporters who are confident that the convention would wind up nominating Carter anyway by a comfortable margin, and that the Carter victory would then appear to have been a freer expression of party sentiment.

But Strauss said the Carter delegates canvassed strongly opposed any plan to release the delegates from their pledge once the battle on the rule was won.