Ted Kennedy still wants to be president, and still thinks he can win that job some day.

In a long, relaxed conversation this weekend, the Massachusetts senator made it clear that the series of resounding primary defeats he suffered in his failed 1980 campaign has not soured him on politics or diminished his ambitions for the White House.

Kennedy, 48, said he had made no judgment about a 1984 presidential race. But if he does run again, he said, he is hopeful that questions about his character will recede in importance, as he thinks they did toward the end of this year's primary campaign.

Kennedy also left the clear impression that his enthusiasm for his party's nominee this year is minimal. He said he would vote for President Carter because "it's important that Ronald Reagan not be successful."

Asked why a voter should choose Carter over independent candidate John B. Anderson, Kennedy thought for a minute, stammered, then said, "Well, I would say that the best opportunity for the defeat of Reagan is with Carter."

Kennedy spoke to a small group of reporters at his elegant McLean home on a bluff above the Potomac. As servants poured coffee from antique silver pitchers, the defeated candidate and his wife, Joan, joined easily in the jokes and laughter as the reporters recalled bungled campaign stops and long-time Kennedy friends who did not support his candidacy. The couple did not look or sound like people devastated by defeat.

Instead, the last son of the party's most successful family, whose father taught all the Kennedy boys that winning is the most important thing, said he had learned something different during the 1980 campaign.

As he met people who were suffering from inflation and recession, Kennedy said, the economic issues he was talking about "took on a life of their own, expressed in human terms that I found very moving, very motivating. . . . The series of [primary defeats], it's not, that's not pleasant, but the forces which motivated me became much more significant, much more powerful, then the result on any given primary night."

Asked if his father would have agreed that issues were more important than primary victories, Kennedy put his arms behind his head and stared at the ceiling with a rueful smile. "My father," he said, "if I told my father that . . . my father -- I'd better not get into that."

Kennedy said the last time he seriously thought he could win the nomination was "pretty early in the campaign."

"It's reasonable to say," he added, "that after the Iowa caucuses and the early primaries the chances of getting the nomination were, were, remote." He said after his upset victories March 25 in New York and Connecticut "there was certainly an upswing, some life to it, life in the campaign."

But he lacked the money to organize major efforts in the following week's primaries in Wisconsin and Kansas, he said, and Carter victories there deflated his hopes again.

Kennedy seemed so untroubled by his defeat that he was able to laugh off a campaign debt that may approach $2 million. Kennedy cannot use his own money to pay it off -- he has already given himself the maximum legal contribution -- but he has a collection of donated art works to sell that could bring in the money he needs.

"You wanna buy some pictures?" he laughed. "We have enough art to run an art gallery for the next four years."

Kennedy was clearly not inclined this weekend to review specific mistakes in his campaign strategy. But he said he probably should have waited longer last fall before formal announcement of candidacy so that he could get pending Senate business off his mind and organize his presidential drive more carefully.

He said he should have chosen a less frenetic stump schedule. And he said he should have developed from the beginning the liberal themes he emphasized later in the campaign. Because he failed to do that, he said, "the differences between myself and the president did not really materialize."

Kennedy complained mildly about Carter's refusal to debate him. "It was a political call, political decision for a political reason," he said. "If there hadn't been the Iranian situation . . . he would have been under pressures to debate. [But] he made the decision, people could understand that he has to be back in the White House."

Kennedy seemed less willing to forgive Vice President Mondale's suggestion that Carter's opponents were unpatriotic in opposing the president's grain embargo.

"His statement that I was unpatriotic," Kennedy said slowly, "I think it was unfortunate, unnecessary, and I didn't like it."

Nonetheless, Kennedy said, he will campaign for the Carter-Mondale ticket this fall. But he would not say when, or how much.

"I'll be active," he said, and then added the caveat that "I see my primary responsibility being the Senate. I mean, I've been away from the Senate . . . . I will be campaigning, but there is an important responsibility there."

On the subject of his political future, Kennedy said he intends to run for reelection to the Senate in 1982, but he said it is impossible to see any further into the future.

"I think it's, I think we've all seen over the period of this year that it's a volatile period," he said. "I think in political life just a few days, let alone a few weeks, are a long, long time. So I don't have now any ideas or intentions . . . ."

But the conversation became much less vague when Kennedy was asked whether he still would like to be president.

"My sense," he said with a forceful nod of the head, "is and has been . . . that in public life it's, that is the position that has the greatest opportunity for influence, probably in the world. I think that [office] has enormous opportunities, for this country, for the people in this country, and for what this country stands for throughout the world. That perception, it doesn't alter or change when the convention ends."

Kennedy said he is "probably least able to make a prediction" about the impact of Chappaquiddick and other "character" questions if he were to run for president again.

But he added that "as the [1980] campaign developed . . . there was much more focus and attention onto the issues, certainly as of June 3, than there had been early in the campaign .. . And [I'm] hopeful, I would expect that if ever we would run again that hopefully that's where we would start off."

At times, the interview took the senator and the press corps right back to the position they were in before Kennedy's 1980 campaign began.For more than a decade leading up to the campaign, he liked to tease the political reporters about his presidential intentions.

During this weekend's interview the reporters talked about Kennedy's appearance on the polium on the last night of last week's Democratic National Convention.

"When you raised your fist toward the Massachusetts delegation," one said, "it looked like you were saying, 'I'll be back.'"

Kennedy greeted this suggestion with a wry chuckle. "Oh, did all that come through?" he replied.

But for the moment, Kennedy appeared to feel relieved and comfortable in the role of noncandidate. Both he and his wife seemed more at ease than almost any time during the campaign. As Kennedy, wearing a denim shirt and a worn pair of blue slacks, gulped coffee and wolfed down pastries, he looked like a man free of cares.

Kennedy flew to Cape Cod after the interview for a family party and an outing on his sailing yacht. It was the first time since last October that he went to the airport without the accompaniment of The Washington Post, The New York Times, the wire services and the networks. On Monday, he is to fly back to Washington with an entourage consisting of a single aide. He will go back to Capitol Hill as just another senator.

Just another senator, that is, whose name happens to be Kennedy and who already appears to be the first choice of a large segment of his party for the presidential nomination in 1984.