BOSTON -- Former Massachusetts Gov. Mitt Romney bowed out of his campaign for the Republican presidential nomination Thursday, making the announcement at gathering of conservative Republicans in Baltimore.

"In this time of war, I feel I have to stand aside for our party and our country," Romney told a crowd of cheering supporters.

"If this were only about me, I'd go on, but it's never been all about me," he said, telling supporters that he had decided to end his race because the nation is at war and Democratic presidential contenders Hillary Clinton and Barack Obama have vowed to pull out of the Iraq conflict and "declare defeat."

Romney said he's stepping aside for GOP front runner, Arizona Sen. John McCain, who supports staying in Iraq, because he doesn't want to see Democrats prevail in the fall election.

"This is not an easy decision. I hate to lose," Romney said.

After Super Tuesday, Romney vowed to carry on the fight for the nomination, but decided against it after a few days of review.

"If I fight on in my campaign, all the way to the convention, I would forestall the launch of a national [Republican] campaign and make it more likely that Senator Clinton or (Barack) Obama would win. And in this time of war, I simply cannot let my campaign, be a part of aiding a surrender to terror," Romney said in his speech to the Conservative Political Action Conference.

He said he was prepared to fight all the way to the convention, just as Ronald Reagan did in 1976, but the fact the country is at war, he said, made all the difference in his decision.

"I disagree with Senator McCain on a number of issues, as you know. But I agree with him on doing whatever it takes to be successful in Iraq, on finding and executing Osama bin Laden, and on eliminating al-Qaida and terror," Romney said.

Romney was lagging in the delegate count behind McCain, after the Super Tuesday elections. He had 294 delegates to the Republican National Convention after the voting concluded Tuesday in 21 nominating contests. Overall, McCain led with 707 delegates, to 294 for Romney and 195 for Huckabee. To become the party's nominee, 1,191 delegates are needed.

"As of today, more than 4 million people have given me their vote for president, less than Senator McCain's 4.7 million, but quite a statement nonetheless. Eleven states have given me their nod, compared to his 13. Of course, because size does matter, he's doing quite a bit better with his number of delegates," Romney said.

Only about 1,200 delegates remained to be won before New Mexico wraps up the nominating process on June 3. That means to secure the nomination Romney would have had to win more than three-fourths of that delegate pool.

Romney, a successful Mormon venture capitalist from Boston who was brought in to save the 2002 Winter Olympics in Salt Lake City and then went on to become Massachusetts governor, declared his candidacy in February 2007, in Michigan, where his father, George Romney, had once been governor.

Romney ran his race on a traditionally conservative Republican "family values" platform that supported the war in Iraq and tax cuts and was anti-Abortion and anti-gay marriage. But he failed to come in first in both the Iowa caucuses and the New Hampshire primary after spending millions of his own money on the race, losing Iowa to former Arkansas Gov. Mike Huckabee, who won the support of evangelicals who were nervous about Romney's Mormon faith.

Romney ended up losing key states such as New York, California and Florida on Super Tuesday, despite having the backing of former Gov. Jeb Bush's aides in the Sunshine State. When former New York Mayor Rudy Giuliani dropped out of the GOP presidential race and threw his support to McCain, the Arizona senator appeared to be winning the support of mainstream Republicans.

"This is not an easy decision for me. I hate to lose. My family, my friends and our supporters ... many of you right here in this room ... have given a great deal to get me where I have a shot at becoming president. If this were only about me, I would go on. But I entered this race because I love America, and because I love America, I feel I must now stand aside, for our party and for our country."

Romney's decision effectively clears the way for McCain's nomination at the Republican National Convention scheduled to take place in St. Paul, Minn.