A sign that political sanity may be creeping into the inner psyche of Sen. Edward Kennedy came during a confidential talk with his advisers last week when for the first time he failed to brush off a discussion about 1984 with an imperious wave of his hand.

On innumerable earlier occasions during his quest for the 1980 presidential nomination, 1984 has been ruled out by Teddy Kennedy as a subject not fit for discussion. This time, he listened as a top aide spelled out the possible verdict on Kennedy if he cuts and runs from a victorious Jimmy Carter after the president's expected nomination Wednesday night. The verdict: you're risking a political death sentence from your party.

The value of that small clue must be weighed against other pieces of evidence in seeking to unravel what most politicans feel is the last 1980 mystery of Madison Square Garden: will Kennedy take a powder when Carter rolls to a first-ballot majority? Or will he sheathe his anti-Carter dagger, throw a perfunctory arm around the man he called a "clone of Ronald Reagan" and support the ticket in the fall campaign?

Kennedy's ambivalence is the only political talk there is here, with time closing in. It is an ambivalence that has marked all the stages of a campaign that began in the stars almost a year ago and sank to the depths after New Hampshire. The senator's play-it-by-ear strategy was exposed once again in Washington last week just after his agents concluded their pact with the White House giving Kennedy's forces -- meaning principally Kennedy himself -- one hour at the rostrum to argue for major changes in the made-by-Carter platform.

Out of the blue, Kennedy suddenly asked: if I should happen to lose the vote on the rules, should I go ahead and speak to the convention anyway?

The self-revelation in that question is staggering. It implied that the senator has truly believed he would win the rules vote and free Carter's delegates of their primary election loyalty pledges, despite all evidance to the contrary. It also raised doubts about his seriousness in asking for the podium for a policy discussion. The core of the White House pact was the proviso, made especially for Kennedy, to allow him to take care directly to the delegates.

Throughout the Kennedy campaign, this ambivalence has confounded politicians trying to figure him out. After the disgrace of losing the New Hampshire primary in February, he had a well-advertised huddle with Sen. Henry Jackson and other defense-oriented Democrats, inviting speculation that he would transform his campaign. Days later, he made his dramatic Georgetown University speech laying the foundation for a totally different campaign: attack Carter for treason to the Democratic party and demand the party's return to what he called its roots -- New Deal, Fair Deal, New Frontier and Great Society politics in an era that clearly has cast that politics out of favor.

The appearence of stark indecision has infuriated major powers in the Democratic Party who have no love for Jimmy Carter. The leader of one major labor union told us that Kennedy's man have "propositioned" him to do "outrageous things" to hurt Carter. "Some of those guys around him are just crazy," this labor leader said. "The Dixie gang has out-slicked them and they don't even know it."

Led by Robert Strauss, Carter's agents here are icing the cake to tempt Kennedy. Conciliation is the rule, starting with the gift of the podium to Kennedy during prime television time Tuesday evening, 100 floor passes instead of the 38 asked for and major compromises in the platform Kennedy wants. The decision to play out all the rope needed to bring Kennedy into the corral was insisted on by Strauss and Hamilton Jordan; Tim Kraft and Jody Powell thirsted for revenge, but they, too, know that without an appearance of reconciliation and some active support from the senator, Carter's campaign might strangle at birth.

That fate for Jimmy Carter may be just what Teddy Kennedy could disgrace the senator, too, ending all that talk about 1984.