Sen. Edward M. Kennedy, buoyed by a surprisingly strong second in Maine's caucuses, entered New Hampshire three days later for a chilling of hopes to revive his challenge against President Carter in this state's first-in-the-nation primary.

Kennedy began the last two weeks of his New Hampshire campaign in the state's southern tier along the Massachusetts border, once considered inviolable Kennedy country. Armed with new issues and an escalating attack on Carter, the senator and his entourage started the day sky-high. But coolness toward Kennedy -- from businessmen, students, factory workers, men and women in the streets -- chilled the senator. As the day wore on, his exuberance departed and his performance diminished.

This experience buttresses the view of Democratic politicians here that the New Hampshire showdown Feb. 26 will have little to do with either organization or issues. It is a choice of character between Jimmy Carter and Ted Kennedy, and all signs encountered by Kennedy suggest the choice now is in Carter's favor.

Although private polls show Carter well ahead with few voters still undecided, the president's managers are not ruling out a close outcome or even conceivably a Kennedy upset, for one reason: southern tier towns such as Nashua, with many residents who commute to Massachusetts jobs and who are not viewed by others in the state as true Hampshiremen. Their erratic voting behavior is credited with the unexpected defeat of statewide incumbents in recent elections.

Kennedy was ready for them, as he was not ready for a similar climactic swing through Iowa two weeks before the caucuses there. In Iowa, he had nothing of substance to say; in New Hampshire, he has reverted to standard liberal dogma. While in Iowa, he flinched from sniping at the president in time of international crisis, he has bludgeoned him in New Hampshire for letting the Iranian hostage crisis go beyond its 100th day.

Much to the delight of New Hampshire's original draft-Kennedy backers, he is running a presidential campaign that now not only is run by George McGovern's old staffers, but echoes McGovern's ideology. Kennedy's basic campaign speech now proposes government control of the economy unsurpassed in a democratic nation. In foreign policy, he talks of "avoiding needless confrontation" with the Soviet Union.

With this message, it was unfortunate for Kennedy that his first post-Maine appearance was a Southern New Hampshire Association of Commerce breakfast. The atmosphere was frigid, but it is doubtful that the temperature would have risen appreciably had his message been less McGovernesque. As the senator entered the hall, the businessmen's wives stared at him with undisguised contempt.

Nor did Kennedy evoke enthusiasm from a forum that has been a favorite for him and his two brothers: the high school assembly. At three high schools, Kennedy's efforts to play on Carter's draft registration proposal generated no excitement. He told an assembly at Nashua High School: A Carter Doctrine that will register you for the draft will send another generation of Americans on to the Persian Gulf to protect OPEC pipelines." The reaction from the students: silence.

On hand-shaking tours through Sanders Industries (an electronics defense contractor) and through downtown Nashua, Kennedy often seemed nervous and, again, stirred little excitement.

By late afternoon, Kennedy's buoyancy had gone flat -- and not just because the reception had been cool. With Carter obviously on the verge of a breakthrough on the Iranian hostages, Kennedy's attack on the president seemed inappropriate. When the White House accused Kennedy of playing politics with the hostage question, Kennedy and his advisers held an emergency meeting at the Timberlane High School principal's office and decided not to back down. But at his next stop, Salem High School, Kennedy seemed subdued.

Nor is it sure that his tough television commercials and personal speeches prodding Carter to come out of the White House and campaign will not backfire. At Sanders Industries, Kennedy perfunctorily asked for help from one women worker in her late-50s, who smiled sweetly. But when we asked her choice, she replied: "Carter. Everybody's for Carter." Why? "You shouldn't talk about a president the way Kennedy does."

Yet it may be his only hope. Another woman worker at Sanders, also close to 60, told us she had been for Carter but was so upset by his refusal to campaign that she would now be for Kennedy -- except for one thing: Chappaquiddick. "That still bothers me," she added.

Although Chappaquiddick was never mentioned during Kennedy's long day, it infests his campaign and his desperate efforts to revive it in New Hampshire. His reborn liberalism, his attacks on the president and Iranian hostage politics all are eclipsed by comparisons of character. Unavoidably, such comparisons are shaped by Chappaquiddick.