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LEBANON, N.H. – Gov. Chris Christie of New Jersey endorsed Mitt Romney’s bid for the Republican presidential nomination on Tuesday afternoon by praising his business and government experience, declaring, “Mitt Romney is the man we need to lead America.”

The endorsement by Mr. Christie, which came hours before the Republican candidates gather here for a debate, marked the latest effort by Mr. Romney to galvanize the Republican establishment behind his candidacy. Mr. Christie got an early start defending Mr. Romney, a former Massachusetts governor, saying that any effort to compare the Massachusetts health care plan enacted under Mr. Romney to the national plan signed by President Obama — as the Perry campaign did in a recent video — was “completely intellectually dishonest.”

In a joint appearance here, Mr. Romney called Mr. Christie “a real hero in Republican circles.”

As the two men took questions from reporters, Mr. Christie said recent comments about Mr. Romney’s Mormon faith made by a pastor who supports Gov. Rick Perry of Texas were unacceptable and out of bounds for a presidential race.

Mr. Romney took the issue one step further and called on Mr. Perry to “repudiate the sentiments and remarks” of the pastor. He added, “I don’t believe that that kind of divisiveness based on religion has a place in this country.”

The two men appeared together in a hotel ballroom here, with their wives sitting in the front row. Mr. Romney reached out to Mr. Christie after his decision last week to stay out of the Republican presidential race. The four of them met on Saturday for more than two hours to discuss the potential endorsement over lunch at the Christies’ private residence in New Jersey.

Mr. Christie intends to plan an active role in the Romney campaign, aides said, and will travel on his behalf, help raise money and serve as a top adviser. He said Mr. Romney was the most prepared candidate in the field, saying, “He didn’t just wander into it.”

“This is somebody who has thought and listened and planned for a good long period of time about what he would do if he was given the honor of being the president of the United States,” Mr. Christie said.

The value of all political endorsements can be fleeting, particularly in presidential races, where a voter’s decision can be deeply personal. Still, Mr. Christie was among the most sought-after figures inside the Republican Party.

“This will not be an endorsement and then move on,” said Russ Schriefer, a top strategist for Mr. Romney, who also helped Mr. Christie win election in 2009. “He will play a very active role.”

Having never run for office nationwide, Mr. Christie does not have a following to hand over to Mr. Romney in crucial early voting states. But his reputation as blunt truth teller in New Jersey could help Mr. Romney with people who doubt his core beliefs.

And Mr. Christie’s endorsement could add to the rush of wealthy donors to Mr. Romney’s side, many of whom had waited nervously on the sidelines for the past few months. Many of Mr. Christie’s biggest backers for a possible run this year were executives who could raise big dollars for Mr. Romney.

Among those Mr. Romney brought on board were James B. Lee Jr., the vice chairman of JPMorgan Chase, who in 2008 raised more than $500,000 for Senator John McCain; Paul Singer, the hedge fund founder and conservative philanthropist; and John A. Catsimatidis, the supermarket magnate and New York businessman.

Privately, Romney aides had said they truly weren’t sure if Mr. Christie was going to seek the Republican nomination — they speculated that even Mr. Christie himself wasn’t sure — and they worried about how Mr. Christie’s entrance would affect Mr. Romney’s ability to shore up support with Republican activists and donors.

Mr. Christie’s explicit backing could aid Mr. Romney’s efforts to lock down establishment Republican donors and build a sense of inevitability around his campaign, as donors recalibrate their plans with the expectation that no other significant candidates are likely to enter the race. It could also help Mr. Romney’s allies recruit new megadonors, like Mr. Singer, to Restore Our Future, the super PAC founded by a group of former Romney aides, which will be going head to head against a well-financed super PAC supporting Mr. Romney’s chief rival, Mr. Perry.

“This is a very significant event for Christie to endorse Romney,” said Jim Nicholson, a former chairman of the Republican National Committee, who announced last week that he would back Mr. Romney “because of his conservative credentials and the following that he has had, the people who were still on the sidelines, who were waiting to see what Chris Christie would do.”

Mr. Nicholson added: “They are a pragmatic bunch. They want to put their money on the nose of the person they think has the best chance of winning. With Christie now saddled up with Romney, that’s going to cause a lot of those people to commit to Romney.”

Still, Mr. Christie’s imprimatur may resonate most among the relatively small group of deep-pocketed Northeast Republicans, many of them Wall Street figures, who were poised to seed the New Jersey governor’s financial efforts had he entered the race. Some of those names have already turned to Mr. Romney, who courted them in recent months and urged them to give him a look if Mr. Christie bowed out. Other Republican donors are likely to remain uncommitted for the time being.

In some ways, Mr. Christie and Mr. Romney are an odd match.

Mr. Christie’s style is bombastic and casual, and at times bullying. He has gotten national attention by taking on the state’s teachers’ unions and by challenging his party’s orthodoxy on climate change, gun control and immigration.

Mr. Romney, by contrast, has spent most of his career as a sharply dressed and stylistically buttoned-down politician. His biggest political liability has been the perception that he does not have rock-solid beliefs on core issues.

But in other ways, the endorsement makes sense. As governors, both men have seen the practical challenges of trying to match ideology with governance.

And Mr. Christie’s other choices seemed like a bad fit. Mr. Perry is a Southern conservative with little in common with his New Jersey counterpart. Representative Michele Bachmann is a firebrand whose style of politics — as well as her position on the issues — is not in line with Mr. Christie’s.

Ray Sullivan, communications director for Mr. Perry, responded to news of the endorsement on Fox News. “Well that’s the way it works in this business sometimes; the Northeast Republicans are sticking together in this case,” he said. “We’ve got a debate tonight that’s supposed to talk about the economy. I’ve got a governor, Governor Perry, who’s got the strongest jobs record in the country, six balanced budgets, cutting billions in spending. That’s really what the voters want to hear about, how to get this economy turned around.”

Mr. Christie made it clear in recent months that he wanted to remain a force in helping to unseat Mr. Obama. Endorsing Mr. Romney will give him a national platform without having to run himself.

Ashley Parker and Nicholas Confessore contributed reporting.