Sen. Edward Kennedy's presidential campaign, spawned by popular demand brief months ago, is now taking on the slightly menacing mien of a spoiler operation whose principal sometimes seems divorced from reality.

The emotional force now driving the senator, the loser in every contest with President Carter except in Massachusetts, derives from this Kennedy conviction; sooner or later, Jimmy Carter can be had if Kennedy only maintains the fortitude, as he put it here, "to stay in the race for the full course."

"Some Kennedy intimates are convinced his cocky, self-confident demeanor in the face of growing adversity is nothing but gossamer, concealing his real purpose of bowing out if he loses next Tuesday's New York Democratic presidential primary in yet another Carter triumph. If so, the performance now being put on by Kennedy commands respect for political gallantry above and beyond any call of duty.

But if Teddy Kennedy means what he seems to be saying and continues a savage, rear-guard action against Carter until the nominating convention in August, many Democrats, including anti-Carter Democrats, will judge him differently. They will view him as a political delinquent willing to plunder his party to prove his rectitude.

Such conduct by the brother of John and Robert Kennedy seemed unlikely, to put it mildly. But his escalating response to his loss in Illinois points hard in that direction, putting the senator in the position of seeking the political execution of Jimmy Carter -- if not before the convention, then in the general election.

Consider Kennedy's answer to a question about what happens when Carter reaches a "mathematical" majority of delegates. It was asked during one of his numerous interviews taped by TV and radio stations here in guarantee of Kennedy's getting good air time without his financially embarassed campaign having to pay for it).

Kennedy's quick reply was that "mathematics" have nothing to do with the matter. Delegations legally bound for Carter could choose not to vote on the first or second ballot, thereby freeing themselves to vote against Carter and, presumably, for Kennedy on subsequent ballots.

That answer happens to be wrong. Pledged delegates who refuse to vote their pledge can be automatically replaced on the floor. But however wrong, Kennedy's answer exactly fit the brave face put on Illinois by Kennedy and his New York handlers, some of whom have been out of national politics since their successful battles for John and Robert many years ago. Illinois, a disaster without mitigation, is being touted by Kennedy as proving that his campaign against Carter's handling of inflation is beginning to take hold. The implication: if Teddy Kennedy just keeps beating on Carter long enough, the voters will get the message.

The dubious quality of this Kennedy hope, however, constantly intruded on the senator during his swing through upstate New York. He was besieged during his dozen or so separate TV and radio interviews with questions about his integrity, his trustworthiness and his reputation, all of which tended to diminish the effect of his attack on Carter economics.

Why, he was asked, in his "negative rating" so high? Kennedy's answer ended with a defense of his married life, noting almost jauntily that he and his wife Joan have been married for 22 years "and many people can't claim that."

This means that even in the liberal, industrial Empire State, the political wounds of Chappaquiddick and other vulnerable points in Kennedy's past are not yet being overlooked.

Any Democratic ward heeler could tell Kennedy that, unless those vulnerable points are exorcised, he is probably the only major Democratic figure in the nation powerless to exploit Carter's own political vulnerabilities, despite a highly effective campaign style that is now smooth, confident and articulate.

Another defeat -- in the New York primary -- ought finally to drive that point home to Kennedy. If such occurs, but he then takes the path that he now is threatening to follow in a futile quest all the way to Madison Square Garden, he will risk ending the political future of both himself and Jimmy Carter and thereby change the face of American politics.