By John Whitesides, Political Correspondent

ST. PAUL (Reuters) - Republicans John McCain and Sarah Palin kicked off a two-month battle for the White House on Friday with a promise that "change is coming," a theme co-opted from their Democratic rivals.

McCain touted his credentials as a reformer and portrayed himself as the real agent of change in the race against Barack Obama as he accepted his party's presidential nomination in an arena filled with supporters waving blue "Country First" signs.

"I don't work for a party. I don't work for a special interest. I don't work for myself. I work for you," McCain said in a speech that included only passing criticisms of Obama after a four-day convention marked by scathing attacks on the Democrat.

"I've fought corruption, and it didn't matter if the culprits were Democrats or Republicans," McCain said as Palin, his surprise running mate, watched from the stands.

The reception for McCain's remarks was more muted than for Palin's fiery acceptance speech on Wednesday, which directed repeated barbs at Obama and drew roars from the crowd, energizing the party's conservative base.

McCain trails Obama slightly in most national opinion polls as they head into the November 4 presidential election, but he promised the Republican faithful he would win.

"And after we've won, we're going to reach out our hand to any willing patriot, make this government start working for you again, and get this country back on the road to prosperity and peace," McCain said.

McCain and Palin joined their families on stage after the speech as balloons and confetti drifted over the arena.

Outside, police arrested 250 anti-war protesters marching to the venue after using flash grenades and teargas to herd them onto a bridge. Inside, McCain was interrupted several times by anti-war protesters. Police hauled two women out of the arena.

McCain has been one of the most outspoken supporters of U.S. military involvement in Iraq.

'DON'T BE DIVERTED'

"Please don't be diverted by the ground noise and the static," McCain said as the protesters were forced out. "Americans want us to stop yelling at each other."

The Obama campaign said McCain had offered more of the same policies of the last eight years under President George W. Bush and the other Republicans.

"He admonished the 'old, do-nothing crowd' in Washington, but ignored the fact that he's been part of that crowd for 26 years, opposing solutions on health care, energy and education," Obama spokesman Bill Burton said.

"He talked about bipartisanship, but didn't mention that he's been a Bush partisan 90 percent of the time," he said.

With the conventions and the selections of running mates out of the way, the next big campaign milestone is the first of three debates, on September 26 in Oxford, Mississippi.

Palin, the Alaska governor, meets Obama's No. 2, Delaware Sen. Joe Biden, in a debate of vice presidential candidates on October 2 in St. Louis.

During his speech, McCain said he had a record of working across party lines on issues. He said Obama had not shown the same ability.

"I've worked with members of both parties to fix problems that need to be fixed," he said. "I will reach out my hand to anyone to help me get this country moving again. I have that record and the scars to prove it. Senator Obama does not."

McCain also recounted his experience as a prisoner of war in Vietnam, where he was beaten and tortured during 5 1/2 years of captivity, and said it taught him to put America first in his priorities.

"I hate war. It is terrible beyond imagination," said McCain. "I'm running for president to keep the country I love safe, and prevent other families from risking their loved ones in war as my family has."

McCain said he recognized that many families had been left behind by the faltering U.S. economy.

"All you ever asked of government is to stand on your side, not in your way. And that's just what I intend to do: stand on your side and fight for your future," he said.

McCain and Palin flew out of Minnesota immediately after the convention ended on Thursday night, heading to Wisconsin for a morning campaign event and later in the day to Michigan and Colorado and on Saturday to New Mexico.

Palin, who has been shielded from most public events and has not done interviews with news reporters since she was picked for the job, heads out on her own on the campaign trail next week.

Obama will campaign in Pennsylvania on Friday.