When Sen. Edward M. Kennedy recognized the inevitable tonight, he still left his victorious rival, Jimmy Carter, with a delicate task of putting the Democratic Party back together again.

It is a task that other presidents have faced before him, most recently Gerald Ford in 1976 when he brought a reluctant Ronald Reagan onto the Republican convention platform in Kansas City to hold Ford's arm aloft in victory.

Some say that Reagan's campaign for the 1980 presidential nonmination began that night. Certainly, what many see as the 1984 Kennedy campaign could begin Thursday in New York City with Kennedy on the platform alongside the man who bested him.

Whether that will happen is not yet known. What is known is that Kennedy has, ever since he arrived in New York, been saying the right things about Republican Reagan from a Democratic Party point of view. What he is yet to do is say the right things about Carter.

But hours before the rules vote that sealed Carter's renomination, a longtime Kennedy operative gave this signal: "Sen. Kennedy will know what to do if he loses the nomination. He won't need someone to figure it out for him. The equation is just as clear for him as it is for Carter."

For Kennedy, that equation requires that he be a good loser. Chappaquiddick he will always have with him. What he does not need is the added liability of party wrecker.

Those who know Kennedy best do not expect him to be a spoiler. He is a Party man, to begin with. And there is no way he can help himself in the future if he becomes known as the Democrat who elected Reagan by undercutting Carter.

In some ways, Carter needs Kennedy even more.

"The symbolism of Teddy is absolutely vital," said a key Carter man early today. "Kennedy has been beating up on us with the old folks, the poor, the working people, the ethnics -- the constituencies where we've got to do well to beat Reagan. That's what makes it difficult for Jimmy to be gracious. That's also what makes it necessary."

It is necessary for Carter because the suspicion lingers, reinforced by his first-term presidency and Kennedy's primary campaigns, that Carter is somehow not "a real Democrat." It is necessary because a president who wants to lead the country must first demonstrate that he can reunite his party. It is necessary because there are places a Kennedy can go where Carter will always be an outsider.

The script calls for a political minuet of the sort followed perfectly by Ford in 1976. It was the first step of his comeback campaign that almost overtook Carter.

At that time, Carter held a huge lead over Ford in the polls, as challenger Reagan does now over Carter. Ford knew he needed Reagan.

With prearranged political generosity, Ford brought Regan on the platform and allowed the loser to make a long and graceful speech that for many of the delegates was the emotional climax of the convention.

"Reagan didn't like Ford any more than Kennedy likes Carter," observed an operative of Vice President Mondale today. "But political reality triumphed over personality differences."

The political reality in this case is that Carter badly needs Kennedy's help in the short run while Kennedy needs to remain a loyal Democrat if he is to have a political future.

This should be enough to bring Kennedy to the convention platform Thursday. And it should be more than enough to persuade Carter to respectfully ask his defeated adversary to join the Carter-Mondale team against the common political enemy.

He will ask very nicely.