Jon M. Huntsman Jr. is overhauling his struggling presidential campaign, aides said, with plans to strike a more aggressive tone against his GOP rivals and President Obama, step up appearances in key states and emphasize his conservatism.

That represents a clear shift in strategy for the former Utah governor, who has presented himself as a candidate eager to follow a more civil style of campaigning and appeal to voters in both parties.

Since Huntsman entered the race with great fanfare last month, he has not converted initial excitement about his candidacy into support, either in polls or among major Republican officials.

In an attempt to jump-start his bid, aides said, Huntsman will highlight his conservative record as governor and directly attack the man viewed as his chief rival, former Massachusetts governor Mitt Romney.

On Thursday, Huntsman replaced his campaign manager, Susie Wiles, with Matt David, a longtime communications strategist steeped in the rapid-response pace of campaigns. In the 2004 campaign, David was one of the aides in the “war room” who devised tactics to attack Sen. John F. Kerry (Mass.), the Democratic presidential nominee, and defend President George W. Bush, who was running for reelection.

Huntsman plans in the next few weeks to highlight what his campaign calls Romney’s weak record on job creation and inconsistency on key issues, aides said.

The campaign also began an initiative dubbed Conservatives for Huntsman to secure pledges of support from 5,000 conservative voters. That represents an attempt to redefine the candidate, whom many GOP voters know mostly as Obama’s former ambassador to China.

“Governor Huntsman is going to be more aggressive about message and strategy and defining differences with Obama and Romney,” spokesman Tim Miller said. “That’s a message that needs to get out in the coming weeks.”

Despite a flurry of media attention on his decision to run, Huntsman’s profile has diminished, in part because he has not successfully described his policy message or his background, some Republican strategists said.

The Weekly Standard, a conservative magazine, recently ran a scathing profile of Huntsman, saying that he missed the meaning of the 2010 Republican victories and that his campaign effectively peaked when he announced his bid.

“He doesn’t have a message that is giving voters a reason to jump his way,” said Mike Dennehy, a New Hampshire political strategist who advised Sen. John McCain (R-Ariz.) before his two presidential primary victories in the Granite State. “He has time to recover, but his campaign needs a new direction and a strong appealing message to conservative Republicans and independents.”

­­Huntman’s aides, who convened in Washington on Friday for a strategy session, said Wiles’s departure signals the second phase of a campaign that they acknowledge got off to a rocky start.

At the same time, they said, Huntsman can come back. The most recent example of a campaign revival is that of McCain, who in 2007 and ’08 resuscitated a nearly-dead candidacy and rebounded to victory in New Hampshire and then won the GOP nomination.

“If he were an extremely well-known person and his numbers were low, that would be cause for concern, but he is still unknown,” said Richard Quinn, one of Huntsman’s South Carolina strategists.

Complicating Huntsman’s path, which hinges on a strong showing in the New Hampshire and South Carolina primaries, is the possible candidacy of Texas Gov. Rick Perry. Polls show Perry ahead of Huntsman and signal that the governor could become Romney’s main rival, a position Huntsman has been hoping to occupy.

Shawn Steel, a longtime GOP fundraiser and member of the Republican National Committee, said that with the possible emergence of Perry, Huntsman has “maybe a month or two to break through the pack.”

“He’s not known by conservatives particularly, he’s not known by party officials, he’s not known by the grass roots,” Steel said. “He just seems to be a nice man.”

One Huntsman aide suggested that the candidate has a shorter window — until mid-August — to break out of the basement in polls. Another aide said the campaign has until October to engineer a turnaround. In a recent poll of Republican primary voters in South Carolina, for instance, not a single person selected Huntsman as the top choice. A new Washington Post-ABC News poll shows him with 3 percent of the vote among Republicans.

Huntsman has been more aggressive of late. At a recent stop in South Carolina, he compared his record of job creation in Utah with Romney’s record in Massachusetts. A top Huntsman aide took to Twitter on Friday to point out Romney’s change in position on signing pledges.

Huntsman will embark on what an aide called a “speech gantlet,” which will take him to New Hampshire, Washington and Florida, where his campaign headquarters is based. On the trip, Huntsman will deliver a retooled stump speech that includes sharper criticism of Obama, his aides said.

Huntsman will spend the first week of August in New Hampshire, then head to South Carolina, where he has been endorsed by former attorney general Henry McMaster, a prominent conservative, and the family of the late governor Carroll Campbell Jr.

Aides said the next few weeks will bring a steady focus on Huntsman’s conservative record — a handbill making the rounds in New Hampshire mentions the word “conservative” three times.

But aides say he will also continue to court young and independent voters.

In marketing Huntsman, aides have clearly taken a page from the Obama 2008 playbook, betting that Huntsman can attract young party members. The Web site makes reference to “Generation H” and introduces Huntsman with the phrase “At Last,” also the title of the song the Obamas danced to at their first inaugural ball.

Huntsman’s biography, which has been packaged in a series of videos on the campaign Web site, highlights his love of street food and motocross.

“It’s going to take a certain touch to reach people who voted for Obama last time,” said Quinn, the South Carolina strategist. “Appealing to the base of the Republican Party is not the same thing as winning in November.”