NASHVILLE, Tenn. — Senator McCain defended his conservative credentials today as rival Mitt Romney claimed he was true to core Republican values in the final push before Super Tuesday. Democratic Senators Obama and Clinton, locked in a tight race, searched for support in the delegate-rich Northeast.

Mr. Romney, the former Massachusetts governor, told voters in a series of coast-to-coast stops that Republicans were telling him, “We don’t want Senator McCain; we want a conservative.”

Mr. McCain leads Mr. Romney in national polls and has seized the momentum and major endorsements after two straight wins in South Carolina and Florida. Yet, some conservatives are uneasy with the four-term Arizona senator who has backed a path to citizenship for illegal immigrants, pushed campaign finance reform, and opposed President Bush’s tax cuts although he now wants to make them permanent.

Campaigning at Boston’s famed Faneuil Hall, Mr. McCain defended his Republican record but insisted he would not hesitate to reach out to Democrats.

“As president of the United States, I will preserve my proud conservative Republican credentials, but I will reach across the aisle and work together for the good of this country,” Mr. McCain said at a rally in Boston.

On the Democratic side, Mrs. Clinton held an emotional reunion with a colleague from the early days of her legal career as a child advocate. The moment came as she revisited her law school days while hosting a campaign event at the Yale Child Study Center where she first pursued her interest in child advocacy.

A New Haven public interest lawyer who worked with Mrs. Clinton as a student, Penn Rhodeen, recalled her showing up on his doorstep wearing purple bellbottoms.

“It was so 1972,” he recalled, praising Mrs. Clinton for her longtime interest in helping children.

“Here is the abiding truth we know — you have always been a champion for children. Welcome home, dear friend. We are so proud of you,” he said.

Mrs. Clinton responded emotionally to Mr. Rhodeen’s praise, at one point wiping her eyes with her hand. But unlike her teary-eyed moment in Portsmouth, N.H., her voice never broke and she tried make light of her emotion.

“I said I would not tear up. Already we’re not on that path,” Mrs. Clinton replied to laughs.

In East Rutherford, N.J., Mr. Obama appeared at the IZOD Center at the Meadowlands, next to the home of the Super Bowl champion New York Giants.

Mr. Obama was introduced by actor Robert DeNiro, who said it was his first time giving a speech at a political event. He was booed when he said that Mr. Obama didn’t have the experience to be president — the experience, he continued, to vote for a war that has damaged America or the experience to be beholden to special interests.

“That’s the kind of inexperience our country deserves,” Mr. DeNiro said.

Senator Kennedy and his niece Caroline Kennedy also appeared on stage with Mr. Obama, who joked that it showed he can unite the country.

“For me to be able to bring a Patriots’ fan to the Meadowlands the day after the Super Bowl is like bringing the lion and the lamb together,” Mr. Obama said. “We can bridge all gaps and all divisions in this country.

“Sometimes the underdog pulls it out,” Mr. Obama said. “You can’t always believe the pundits and prognosticators.”

While normally eschewing poll results, Mr. Romney cited one unnamed survey he said showed him leading in California, and another he said confirmed a neck-and-neck race in Georgia.

“It’s a very tight race. A lot of people said it’s just going to be, you know, a very easy race for Senator McCain. But you know what’s happened? Across the country, conservatives have come together and they say, you know what? We don’t want Senator McCain; we want a conservative,” Mr. Romney said today at the Pancake Pantry in downtown Nashville.

Rep. Marsha Blackburn, Republican of Tennessee, said in introducing Mr. Romney: “We know that a lot of freedom-loving, flag-waving people are going to find their way to the polls on Tuesday.”

Some two dozen states vote tomorrow, from New York to California to Alaska. At stake for the Republicans were 1,023 delegates, up for grabs on the Democratic side — 1,681 delegates to the national convention.

Asked if he could continue his candidacy if he lost California, Mr. Romney said: “It depends on what the numbers show. I’ll take a look at what we’re seeing, and I expect to win, and I’m going to only forecast for victory and success as I go across the country.”

Mr. Romney predicted that he and Mr. McCain will divide the spoils in California.

“I think you’re going to see a growing crescendo of Republican conservatives getting behind my candidacy. Right now that hasn’t entirely happened. There are a few states where some folks are holding out for another conservative voice, but my guess is that after Tuesday, you’re going to see this coalesce into an entirely a two-person race and in that setting, I think I win,” he said.