Standing amid the alien colonial splendors of Faneuil Hall, before a women's rally for Sen. Edward M. Kennedy (D-Mass.) today, Walter F. Mondale deadpanned his opening lines.

"You are wondering why I am here," the former vice president said, "and I have some perfectly good explanations. Your senator, Ted Kennedy, is in a difficult campaign for reelection, and he is clutching my coattails so I can haul him over the victory line."

The sally was met with slow-starting laughter and applause. Kennedy needs as much help in Massachusetts as does Princess Diana with her doting public in Britain. Kennedy expects his usual landslide, this time over businessman Ray Shamie.

Nonetheless, Kennedy gladly accepted Mondale's unexpected offer of a day of joint campaigning. Both men know that Democrats are already undergoing premonitory dread about 1984 and a repeat of the civil war of two years past.

Mondale has been taken aback by ferocious antipathy toward former president Carter that he has met everywhere in his travels. It is obvious from the polls that Democrats do not share Carter's view of Kennedy as the spoiler of 1980.

For Kennedy, the appearance of former and future rivals as buddies meant a show of party harmony that further isolates Carter in his efforts to rally resentment against his 1980 challenger.

So the two men were exceptionally merry and generous with each other in their day-long tour of constituencies for which they may eventually compete. Kennedy paid tribute to Mondale's contribution toward "sensitizing the country to the needs of women and children." In his turn, Mondale praised Kennedy for giving "a voice to the powerless and voiceless in America."

They extend well-rehearsed gibes about their unannounced intentions for the presidency. Kennedy said it was "appropriate" for Mondale to come to Massachusetts -- "he has flown over it so many times on his way to New Hampshire." Mondale said he wants to "keep Ted in the U.S. Senate."

The swapping of gag gifts began at a dedication of the Boston Floating Hospital, where Kennedy gave Mondale a "Kids for Kennedy" T-shirt. At Faneuil Hall, Mondale, having noted that Richard Nixon has predicted that Kennedy will be the nominee if he loses weight, presented him with a year's supply of free sundaes from Brigham's, a local ice-cream chain.

At every stop, Kennedy was careful to say of his guest, "He has been my friend, he is my friend today and he will be my friend, come what may."

Mondale was confronted by the hidden agenda of his mission on the steps outside the crimson-carpeted Harvard Club, and there the day's only rub developed. The huge press corps attracted by the season's most diverting and provocative political spectacle cornered Mondale and asked him about Carter's harsh attacks on Kennedy. Most recently, on ABC-TV's "20/20" program, Carter said again that Kennedy "can't be trusted in a crisis."

Mondale, who elsewhere expressed disapproval of the "politics of blame," responded briskly, "That's history. I'm interested in the future."

"Not history," a reporter reminded him. "He said it last week."

Suddenly the little knot became aware of the presence of Kennedy who had slipped into position next to Mondale.

"What are you doing?" he asked in the slightly annoyed tones one would use with an errant child. "You are having a press conference up here by yourself. You left me in the car."

"C'mon," he said, grasping his guest by the arm, "help me get reelected."

"That's what I'm doing," said Mondale, relieved to be rescued from explaining the vituperations of his former boss. "And I'm doing a great job."

Mondale, speaking well, without the cracks and whines that sometimes mar his delivery, did not find a single occasion to mention Carter's name -- not even when he spoke, more eloquently than Kennedy, on Kennedy's issue -- the nuclear freeze. He reeled off evidence that "Reagan has a thing about disarmament" but, in the list of presidents whose arms agreements he has opposed, did not specify Carter.

For many Democrats, Kennedy's well-known personal problem is matched by Mondale's political problem, the Carter drag. If he disavows the former president, Mondale can expect a shower of poisoned arrows from Plains. He is plainly hoping that actions speak louder than words: Carter trashes Kennedy, Mondale campaigns with him. Even Bostonians flinch at the choice.

One man, at the hospital dedication, reacted with amazement to a question about his preference: "I'm for Kennedy, of course." But a young woman, who had volunteered for Kennedy in 1980, said, "I couldn't go through it again. With him, it comes down to a question of personality."

Mondale had a chance to show the Kennedy faithful that, if they can tear themselves away from their idol, "safe, comfortable Fritz" is there to settle down with. If, that is, he can distance himself from a president they want to forget.