BOSTON (AP) _ Sen. Edward M. Kennedy is finding himself doing some unusual things this campaign - hanging out with Aerosmith, going negative and running neck-and- neck with a Republican.

Kennedy's opponent is Mitt Romney, an energetic, clean-cut millionaire who is convinced - and has convinced other Republicans - that 1994 is the year Kennedy comes home from Washington for good.

''After many years there are some serious questions being raised, indeed for the first time among his own supporters, about whether it would be best for him to continue or for him to be replaced,'' said Paul Watanabe, political science professor at the University of Massachusetts-Boston.

Both candidates, for different reasons, are banking on a key premise: Voters know who Kennedy is and what he has done.

Kennedy hopes they know him as a powerful senator who has fought for education, health care, job training, child care and other issues, and repeatedly steered federal dollars to Massachusetts.

''He says longevity, meaning experience, is not a vice but a virtue,'' Watanabe said. ''The prime virtue attached to that is clout.''

But the picture painted by Romney, son of former Michigan Gov. George Romney, is of an old, out-of-touch liberal pol who has been in Senate far too long, pushing massive government programs that exacerbate problems rather than solve them.

''He's just too associated with the old, discredited liberalism,'' said Todd Domke, a Republican consultant.

Romney spent last Thursday chatting up Republican fund-raisers in Washington. Nevertheless, to protect his ''outsider'' image, Romney says he doesn't want Republican bigwigs coming to Massachusetts to campaign.

''This race will be between Mitt Romney and Ted Kennedy and it'll be run from Boston to Springfield. What Washington says really is going to be irrelevant,'' said Gary Koops, spokesman for the National Republican Senatorial Committee.

Kennedy, though, has relied on several big names. And unlike many Democrats around the nation, he has not been loathe to embrace the Clintons.

Hillary Rodham Clinton attended a fund-raiser for the senator in Boston on Friday, and the president was set to attend a gathering this week at Kennedy's home in Virginia.

He also has made an effort to woo younger voters who haven't been touched by the Kennedy mystique, campaigning with celebrities like actor Alec Baldwin and nephew John F. Kennedy Jr.

Earlier this month, the Boston hard rock group Aerosmith performed at a Kennedy fund-raiser.

And, for the first time in 32 years, Kennedy has run negative ads, hitting Romney for his role as a venture capitalist. In an increasingly personal exchange, the two have traded charges for two weeks.

''Mitt Romney - he's misled us twice, with negative ads distorting Senator Kennedy's record and phony claims about his own,'' the announcer in Kennedy's most recent commercial intones.

''Ted Kennedy's distorted negative attacks on me are wrong,'' Romney responded, ''and more than anything else, these cynical old-style politics prove he's been in Washington too long.''

Romney won the GOP nomination in a landslide last week over businessman John Lakian, who was crippled by questions about his honesty.

A poll taken just before the primary showed the 47-year-old Romney and Kennedy, 62, in a statistical dead heat. Two polls released Sunday confirmed that finding.

Romney's image - a father of five who married his high school sweetheart and doesn't drink, smoke or swear, has made millions in the business world and sounds as enthusiastic as a motivational speaker - holds great appeal for many Republicans.

Voters will contrast that, political observers say, with what Kennedy once called ''the faults in the conduct of my private life.''

Also working against Kennedy is an anti-incumbent sentiment that has led 15 states to vote to limit the number of terms elected officials can serve. A term-limits question is on the Massachusetts ballot in November.

While not endorsing Romney, Dan Hunter, director of the state chapter of United We Stand America, the organization founded in the wake of billionaire Ross Perot's independent presidential bid in 1992, said the group would be ''elated'' to see Kennedy voted out.

''There's a lot of disenchantment out here, and one of changes that would make it better is to see some of the old dogs out of there,'' Hunter said.