Mitt Romney is planning to fortify his communications and messaging team by adding seasoned operatives, advisers close to the campaign said Thursday, after withering criticism from prominent conservative voices that his insular team has fumbled recent opportunities.

Romney’s advisers insisted that he would keep his inner circle intact amid growing concerns about the Republican presidential candidate and his campaign. The tempest began with a weekend tweet from media tycoon Rupert Murdoch and burst Thursday onto the pages of his newspaper the Wall Street Journal, as its conservative editorial board opined that Romney’s advisers were “slowly squandering an historic opportunity” to beat President Obama.

By day’s end, talk radio host Laura Ingraham had asked listeners whether the vacationing candidate should “get off the jet ski,” and influential commentator William Kristol, who recently returned from a private retreat with Romney and his senior strategists, had bemoaned the campaign’s “dangerous self-delusion.” Without a course correction, Kristol posited, Romney would suffer the same fate as the last two presidential nominees from Massachusetts, Michael Dukakis and John F. Kerry, both Democrats.

Romney’s advisers strongly rejected the course-correction suggestion but said they have been in the process of recruiting more political muscle to his Boston-based headquarters.

The campaign plans to bolster its rapid response and overall messaging operations and to assemble a senior staff for the eventual vice presidential running mate, according to strategists close to the campaign. They said some Republicans who have been informally advising the campaign may assume more official duties, including appearing as surrogates on television. The strategists said the moves could be announced as early as next week.

One GOP strategist not working for Romney said, “The campaign needs to show the GOP elite world and the media a lot of competence going forward or this shake-up talk will only get louder and continue.”

There are no plans, however, to alter Romney’s core team of advisers, most of whom have worked for the former Massachusetts governor for years, and campaign officials said it was highly unlikely that Romney would demote or fire any of his senior staffers.

“I don’t sense any panic. I don’t sense that any heads are going to roll,” said Tom Rath, a longtime senior adviser to Romney. “The idea that this guy at this point having gone through what he’s gone through is going to somehow scramble the eggs on the team — they don’t know Mitt Romney.”

“The idea that somebody other than Beth Myers, Eric Fehrnstrom, Matt Rhoades, Stuart Stevens and Peter Flaherty are going to call the shots, it’s just plain wrong,” Rath said, ticking through Romney’s closest advisers, including Rhoades, the campaign manager, and Stevens, the chief strategist.

Gail Gitcho, the campaign’s communications director, said, “Governor Romney respects the team that he has, and he has full confidence in their abilities.”

For Romney, the Journal critique Thursday was a brutal exclamation point after two difficult weeks for his campaign. One Republican strategist who works closely with the campaign acknowledged tactical mistakes, especially the campaign’s handling of a Washington Post report about Bain Capital’s investments during Romney’s tenure at the firm in companies that moved jobs overseas.

The news article became the basis of harsh attacks from Obama and ads by his campaign that threaten to undermine Romney’s business credentials.

The Journal wrote in its editorial that Romney’s campaign was too slow to respond and said of Obama’s new attacks on Romney’s foreign bank accounts: “If the Boston boys let that one go unanswered, they ought to be fired for malpractice.”

The “Boston boy” who came into particular focus was Fehrnstrom, Romney’s longtime chief spokesman, who on Monday put the campaign at odds with GOP talking points by saying that the individual mandate in Obama’s health-care law requiring people to buy insurance or pay a penalty is not really a tax.

On Wednesday, Romney belatedly got in line with the rest of his party, saying that the federal mandate is a tax because the Supreme Court ruled it so and that what the Supreme Court rules is the law of the land. The Journal wrote that “the campaign looks confused in addition to being politically dumb.”

Ingraham led the griping on her radio show Thursday, accusing Romney of hiding from a public debate over Obama’s health-care law by taking a week-long vacation with his family at their lakefront compound in Wolfeboro.

“I don’t even think this is his fault,” Ingraham said. She added, “This is the advisers telling him, ‘Oh, it’s fine. Take a week.’ There’s no week to spare. We have a country to save.”

Some of Romney’s top supporters voiced confidence in his team.

Former New Hampshire governor John H. Sununu, a onetime chief of staff to President George H.W. Bush, said in an interview, “I’ve been through enough of these to know that there’s an occasional bump in the road. The art form of campaigning is to have fewer bumps in the road than the other guy and having more high points, and I think this campaign demonstrated that in the primary process.”

Anthony Scaramucci, a New York financier and one of Romney’s top fundraisers, said he recently gave Rhoades and Lanhee Chen, the campaign’s policy director, copies of a new book, “The Candidate” by Samuel L. Popkin. Scaramucci said the book discusses two ways that campaigns get derailed: by committing consistent gaffes or by being overly baited by the opponent.

“The campaign has done a very masterful job of trying to keep the message on jobs and the economy,” Scaramucci said. “They’ve done an incredibly effective job of getting the governor to where he is right now. They’ve stayed on message. They haven’t been overly baited.”

Rath, a veteran of presidential campaigns, suggested that the hand-wringing was only natural in the ebbs and flows of campaigns.

“Running a campaign is like being the manager of the [Boston] Red Sox,” Rath said. “Everybody thinks they know how to do your job better than you do.”

Chris Cillizza in Washington contributed to this report.