PROVIDENCE, R.I. — Republican campaign dropout Mitt Romney endorsed John McCain for the party's presidential nomination and asked his national convention delegates to swing behind the likely nominee.

"Even when the contest was close and our disagreements were debated, the caliber of the man was apparent," the former Massachusetts governor said, standing alongside his former rival at his now-defunct campaign's headquarters. "As a party, we come together."

"We all know this was a hard campaign ... and now we move forward, we move forward together for the good of our party and the nation," said McCain, who was campaigning in Vermont and Rhode Island earlier in the day and added a flight to Boston to accept the endorsement.

The two met privately before appearing together at a brief news conference.

McCain effectively sealed the nomination last week when Romney withdrew from the race; only former Arkansas Gov. Mike Huckabee and libertarian-leaning Texas Rep. Ron Paul remain. But neither has a chance to catch McCain in the convention delegate hunt.

In early primaries and caucuses, Romney collected 280 delegates. The number is enough to move McCain close to the total of 1,191 needed to clinch the nomination a full nine months before the November general election.

Romney's nod of support capped a bitter yearlong rivalry between the two men over the party's nomination. Romney criticized McCain in television ads in New Hampshire, and both candidates mixed it up almost daily during campaign events and debates. Neither is especially fond of the other.

Over the past year, Romney cast McCain as outside of the GOP's conservative mainstream and a Washington insider who contributed to the problems plaguing a broken system. McCain, in turn, argued that Romney's equivocations and reversals on several issues indicated a willingness to change his positions to fit his political goals.

The clash effectively ended on Feb. 5, when McCain won a string of big-state primaries from coast to coast.

Officials said the former Massachusetts governor made his decision to back McCain earlier in the day, citing a desire to help the Arizona senator wrap up the nomination before too much more time passed and while Democrats still did not have a nominee.

McCain is on a steady march toward amassing the 1,191 delegates he needs, but Huckabee has proven an unexpectedly durable challenger. With a strong appeal to evangelical conservatives, Huckabee defeated McCain in two out of three states that chose delegates last weekend, and ran a far stronger race than expected before losing the Virginia primary on Tuesday.

The senator began the day with 843 delegates, to 242 for Huckabee.

While Romney can ask his delegates to support McCain, he won't be able to simply hand over all 280 delegates. Many are from caucus states that won't select the actual delegates until state conventions this spring. Those delegates will be selected by people who supported Romney in the initial caucuses; the direction they go depends on whether they follow Romney's lead in endorsing McCain.

In other states, the delegates are bound to Romney, and their fate is governed by state party rules. In states like Montana, where Romney has 25 delegates, they would be free to support whomever they choose after Romney releases them.

Six of Romney's delegates are members of the Republican National Committee who continued to endorse him even after he dropped out of the race. These RNC members are free to support any candidate they choose at the convention, and not all of them appeared eager to endorse McCain,

"I will support our nominee," RNC member Diane Adams of Indiana said simply.