What is Edward M. Kennedy up to?

"I think," the Massachusetts senator replies, "that the interpretation is best left to others." Or, let them all guess.

In fact, Kennedy, nearly 47, is like the child in the nursery rhyme who "could if he would, but he won't." He could, the polls say, trounce the sitting president of his party in 1980 if he would just say he is running. But he won't -- or at least he says he won't.

But he also won't do anything to squelch the speculation. He clearly enjoys keeping the option open and the White House on Edge. That gamesmanship greets visitors the moment they enter his office.

"It's about time The Washington Post got here," the receptionist says with a grin. "He's been on the front page of the Star the last eight days running."

Most of those stories reported Kennedy's proposed budget cuts. Day after day, Kennedy or members of his huge and hyperactive staff produced some jibe or comment, analysis or rebuttal that put him at odds with Carter -- and into the papers.

What about that? Been blown out of proportion, Kennedy replies. "We're talking about $4 billion or $5 billion of difference in a budget of $530 billion," he notes. But he also confirms -- by refusing to deny it -- that he warned his staff recently not to let him appear too critical of Carter. "Let's cool it," one associate quoted Kennedy as saying.

The ironies here are juicy. Kennedy gets enormous publicity for criticizing the administration, yet the record shows that he is among Carter's staunchest supporters in the Capitol on roll-call votes.

But when asked if he has consciously passed up a chance to criticize the administration -- if he ever ducked one because he did not want to look too critical -- the senator laughs.

"Not that I can think of," he replies.

And would he dispute John B. Connally's observation that "if you have ever seen a man positioning himself to run for president, Sen. Kennedy is"?

This provokes the line that "interpretation is best left to others." A little later Kennedy adds that "my position is clear," but of course it isn't, and he makes no effort to clarify it further, except to repeat what he has often said before, that he anticipates a Carter renomination and a Carter reelection in 1980.

This banter passes back and forth between Kennedy and two visitors to the Dirksen Office Building, in the huge, airy office that Kennedy has inherited from Sen. James O. Eastland (D-Miss.) along with his new job as chairman of the Judiciary Committee. During a 25-minute interview the senator doesn't complete very many sentences. He plays with his eyeglasses a lot. He shifts around in his chair.

One visitor asks if he is impatient with all the questions about his presidential ambitions. "I can't say I'm impatient," he replies. "Realistic, I guess."

Well, does he foresee a time when he may have to make a categorical denial of candidacy, something beyond his stated expectation the Carter will be reelected?

"I certainly don't see that as necessary now, or in the foreseeable future," Kennedy replies.

Why should he rule anything out? a close associate asks. "Frankly, he encourages the talk -- it's helpful when he has to deal with [Senate Majority Leader Robert C.] Byrd (D-W. Va.) or the White House." Others around Kennedy agree enthusiastically. They ride the wave and enjoy the view from the creat. "It's just good politics," one says.

Kennedy may occupy a unique political role in the history of the Republic. He carries what amounts to a royal name that guarantees high visibility and public attention. He has a national following at a time when even the president can't say that with confidence. He is probably the biggest celebrity in the nation's public life.

The pollsters report that Kennedy is running far ahead of Carter among Democrats. A Los Angeles Times poll in New Hampshire (where the koy early presidential primary has often been carried with write-in votes) found in December that Democrats favored Kennedy 57 to 21 percent over the president for the 1980 nomination. Nationally a Lou Harris survey, also in December, gave Kennedy a 56 to 39 percent lead over Carter among Democrats.

An activist by instinct, surrounded by an aggressive, competent and energetic staff, now blessed with a major committee chairmanship as well as membership on three other useful committees, Kennedy is places to become one of the titans of the Senate.

He has more than 70 people working for him, including an inner circle of about 10, at least some of whom see themselves as the equivalent of a White House staff. ("It's a better group than Carter has around him," one senator friendly to Kennedy said recently.)

Kennedy encourages his associates to find areas worthy of his attention or involvement, a mode of operations that augments the flow of news releases and position papers on a wide variety of subjects.

For example, during January Kennedy (in person or in a statement) spoke or acted on urban problems, oil company pipeline divestiture, energy policy in general, dental care, tax loopholes, civil rights issues, the confirmation of federal judges, trucking deregulation, the security of Taiwan, the kpresident's 1980 budget, the Law Enforcement Assistance Administration, victims of crime, antitrust policy, relations with Mexico, the role of women in American life and a host of local Massachussetts issues.

Kennedy concedes that a big, agressive staff, with links to many outside interest groups, keeps pushing him to issues. But he also says that "after 16 years here, I've developed more understanding of the issues. And there are areas of public policy where there really are large gaps in leadership."

Some friends see him filling the vacuum left in liberal leadership by the death of Hubert H. Humphrey. But others think he really has his eye on supplanting Jimmy Carter.

Some of Kennedy's closest associates -- people who share the traditional liberalism that the senator still espouses, despite the current political fashions -- doubt that Kennedy's positions on issues make much difference to his popularity. "He's Kennedy," one said. "He can talk about whatever he wants to."

But what Connally said about Kennedy's "positioning himself" is certainly borne out by the senator's schedule. In the past year, there has been hardly a consituency or a cause important to the Democratic Party's left with which he has not publicly identified.

Going back to January 1978, his speeches outside the Senate read like an itinerary of the issus and organizations of the liberal movement. Some of them:

The Committee for a Sane Nuclear Policy, the Consumers Conference, the United Auto Workers, the AFLCIO Committee on Political Education (COPE), the American Civil Liberties Union, the U.S. Conference of Mayors, the National Medical Association, the National Governors Conference, the NAACP, the Energy Coalition, the Congressional Black Caucus Dinner, the Machinists legislative conference, the National Organization for Women, the Martin Luther King Jr. anniversary dinner, and, of course, the Democratic miniconvention in Memphis.

All this, puls a round of hearings in major cities (and madia markets) on the national health insurance plan, highly publicized trips to China, the Soviet Union and western Europe, a fall campaign schedule that carried him to a dozen states and a steady stream of media interviews.

And if Kennedy will not signal an intention to run, he has made moves that tantalize those who are hoping fro his candidacy. One of those was the firing last fall of Carl Wagner, a widely admired political organizer who reportedly chose to work for Kennedy instead of taking a job with the Carter administration Asked about Wagner, Kennedy says he has usually had someone on his staff responsible for liaison with politicians and political groups around the country.

The Kennedy potential intrigues a variety of Democrats dissatisfied with Carter's leadership, and they spend time concocting strategies that would put him in the race without his having to take the first step.

A favorite plot, described by William Winpinsinger, the outspokenly anti-Carter president of the International Association of Machinists, calls for the election of nominally uncommitted but openly pro-Kennedy delegates in next winter's Iowa precinct caucuses the first step in the 1980 Democratic nomination process.

A political consultant sympathetic to the Kennedy cause says it would be possible for dissident labor, farm and liberal groups to win 50 percent of the Iowa delegates on a pro-Kennedy uncommittee slate, against candidacies by both Carter and Gov. Edmund G. (Jerry) Brown Jr. of California.

That would send an unmistakable invitation for him to run, the consultant says.

The same source notes that New Hampshire -- with its write-in tradition -- comes right after Iowa, followed a week later by primaries in four New England states where Kennedy is extremely popular.

But Kennedy says, "I have never heard that discussed. I think it's very difficult to elect uncommitted people anywhere."

Another favorite plot has Kennedy hanging back unless and until Brown beats Carter in some primary -- then jumping in, not as the party-wrecker but as the safety man in a stop-brown campaign.

But again, when asked, Kennedy rejects the idea that Brown's candidacy would affect his decision. "It would not," he says. "I'd expect that if he runs, the president would beat him."

"Obviously," he adds, "the political scene is continually evolving and changing. But some things don't change. The president will be a candidate and he will be renominated -- and I think he'll be reelected."

Among the close friends who occasionally sit down with Kennedy at his McLean home to share their views on the state of the world and the Democratic Party are Washington lawyers John Douglas and Fred Dutton; his former administrative assistants, Paul Kirk and David Burke; Frank Mankiewicz, the Robert Kennedy press secretary who now heads National Public Radio, and, occasionally, a member or two of his current Senate starff.

Most of those in the inner circle who will talk about their views say Kennedy's 1980 candidacy is unlikely. "It's perfectly natural for Ted to be thinking about it," one of them said. "but he seems perfectly comfortable where he is for now."

Another says he finds Kennedy "much more interested in talking about issues than the polictics of issues. The talk is about the energy bill or Mexican gas, not delegate-selection rules."

Kennedy's friends and associates seldom raise the negatives that would inevitably play a role in a decision to run for president. They tend to discount the drowning accident at Chappaquiddick, the problems of his marriage, the concerns of his family over the safety of the last Kennedy brother. One associate said Kennedy probably thinks about those things a great deal more than the people around him do.

Those in the inner circle who are personally very critical of Carter's leadership say they hope Kennedy will run next year. But none of them says he has urged that course on the senator, and none says he knows of anyone close to Kennedy who is pushing him to run.

"My position," Kennedy says, "is unchanged." And it is one he is obviously enjoying -- no matter where it leads. Or when.