(Updates with Romney in California, changes dateline)

By Claudia Parsons

LONG BEACH, Calif., Feb 4 (Reuters) - Sen. John McCain and self-proclaimed underdog Mitt Romney argued on Monday over who is the real conservative the day before Super Tuesday voting that could crown a presumptive Republican White House nominee.

Battling to stay in the race, Romney made a last-minute dash back from the east coast to California -- a battleground state where he was pinning his hopes on recent polls showing him edging ahead of the Arizona senator.

"One of the reasons I came back to California is that I know that Republicans in California care very deeply about the heart and soul of the Republican party," he said at an evening rally in an aircraft hangar at Long Beach, California.

Romney, a former Massachusetts governor, sought to stir discontent among conservatives who are skeptical about McCain's record of having voted against President George W. Bush's tax cuts and his moderate views on illegal immigration.

"A lot of people said it is going to be a very easy race for Senator McCain. But across the country conservatives have come together and said, 'You know what, we don't want Senator McCain. We want a conservative to be in the White House'," Romney said in Nashville, Tennessee.

McCain ripped Romney at a campaign rally in Hamilton, New Jersey, saying Romney presided over a "big government, mandated health care plan" as governor of Massachusetts.

McCain said he has long favored cutting federal spending and is a strong proponent of facing down the challenge of Islamic extremism -- positions he said are at the heart of conservatism. "So I'm proud of my record in the Senate as a staunch conservative."

McCain has a lead over Romney in many states and has a chance of emerging from the Tuesday nominating contests as the presumptive Republican nominee.

But he is in a close battle with Romney in California, a big prize among the 21 states that are holding Super Tuesday contests for Republicans in their race to determine who will face the Democrats' choice in the November election.

"We're going to hand the liberals in our party a little surprise on Tuesday evening when we take California, we take Georgia and we take states across the country," Romney said at a rally in Atlanta, Georgia.

LAST-MINUTE CHANGES

Both Romney and McCain made last-minute changes to their schedules to appear in California one more time -- Romney on Monday night and McCain in San Diego on Tuesday afternoon.

"If I win California that means you're going to have a conservative in the White House," Romney said in Nashville.

McCain made no pledges to win the state, saying he was confident he would do well across the country but that Romney had spent millions on advertising in California. "We know it's tough. But when you look all across the East and the South and across the Midwest, we're very optimistic," he said.

While trying to placate conservatives, McCain also made clear he was seeking the votes of independent and moderate Republicans who have helped propel him to the lead.

"I will preserve my proud conservative credentials but I will reach across the aisle to work with the Democrats for the good of this country," he said in Boston.

In New York, McCain picked up the endorsement of former New York Gov. George Pataki. He also appeared with Democrat-turned-independent Sen. Joe Lieberman of Connecticut and former New York Mayor Rudy Giuliani, who dropped out of the presidential race last week and endorsed McCain.

Romney forecast the campaign would be only half-way through after Tuesday night. "This race is going to go on," he said.

"I think you're going to see we're going to pick up a bunch of delegates tomorrow, I'm going to get a bunch of states and it's going to show the kind of momentum that I need to show to be able to get this nomination."

Romney planned to fly back overnight to West Virginia and then to his hometown of Boston to vote.

"I'm definitely the underdog compared to Senator McCain," he said in Atlanta. "But the nice thing about being the underdog is we typically win." (Additional reporting by Steve Holland with McCain, editing by Chris Wilson) (To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at http:/blogs.reuters.com/trail08/ (Editing by Cynthia Osterman)

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