MOUNT PLEASANT, S.C. -- Democrat John Kerry formally launched his presidential candidacy Tuesday by offering his Vietnam War-hero credentials and Senate tenure as an alternative to President Bush's record. His campaign at a political crossroads, he denied any shakeup was coming.

"Every day of this campaign, I will challenge George Bush for fundamentally taking our country in the wrong direction," Kerry told the crowd on a steamy morning. "George Bush's vision does not live up to the America I enlisted in the Navy to defend."

The stars-and-stripes announcement with the aircraft carrier USS Yorktown as a backdrop and Kerry's wartime comrades at his side came amid talk of changes in the campaign. Kerry first said there were no plans "at this time" for changes, then gave a mixed review of his staff.

He then issued a terse statement after meeting with top aides.

"I have confidence in my campaign," Kerry said. "I have assembled a great team that is going to beat George W. Bush, and any rumors to the contrary are completely erroneous and there will be no changes."

Aides speaking on condition of anonymity said Kerry delivered that same message to top staffers in private. The distraction was the last thing Kerry needed on a day he hoped would be filled with the major themes of his campaign. The issue arose when he was questioned about looming changes.

Kerry said he has no immediate plans for an overhaul, but gave his staff mixed grades.

"I think they've done a spectacular job on a lot of things. I think there were some things we could have done better," Kerry said upon arriving in Iowa, the second stop on his announcement tour.

The four-term Massachusetts senator was once viewed as the Democratic front-runner in the crowded field of nine, but that perception evaporated in the heat of party rival Howard Dean's summer surge.

Kerry's political free-fall has prompted a fresh round of finger-pointing in his deeply divided campaign and has the candidate considering changes, according to several campaign officials who spoke on condition of anonymity.

Kerry said he has not considered a shake-up, though he sounded as if changes could be made.

"You always hold the possibility open if something's not working you do something," Kerry said. "I always reserve the right to do what I need to do to run a good campaign." Hoping to put the issue to rest, Kerry then issued his denial.

The tone of Kerry's speech, in fact, was the subject of fierce internal debate within the campaign over whether to focus on his resume and Bush's performance, or lambaste Dean. The former Vermont governor has grabbed a hefty 21-point lead over Kerry in the latest New Hampshire poll, a crucial state for the two New Englanders. Dean has built momentum with his anti-war, anti-Washington themes and successfully tapped the Internet for fund raising and supporters.

Kerry opted to devote much of his speech to his military service, years as a Massachusetts senator and Bush's record on the economy, the environment and national security. He took a few subtle swipes at Dean.

"Some in my party want to get rid of all tax cuts, including those for working families," he said. "That's wrong. We need to be on the side of America's middle class and I've proposed a tax cut for them because it's the right way to strengthen our economy."

Dean favors a repeal of all of Bush's tax cuts.

Kerry also alluded to Dean's opposition to broadening gun-control laws, which has made his campaign more acceptable to groups such as the National Rifle Association.

"Our party will never be the choice of the NRA and I'm not looking to be the candidate of the NRA," Kerry said. "Courage means standing up for gun safety, not retreating from the issue out of political fear."

At the White House, spokesman Scott McClellan declined to respond to Kerry's criticism of Bush, saying, "I think I'll leave the politics to the Democrats in their primary. The president's continuing to focus on the people's business."

Kerry's speech was written by the senator and Democratic consultant Bob Shrum with little input from the rest of his staff. Shrum, who recently joined the campaign, has been at odds with other senior aides who put the early pieces of Kerry's campaign together.

Aides say the weeks-old rift has grown amid Dean's surge. One senior adviser, speaking on condition of anonymity, said Kerry is considering changing or clarifying the duties of some of his top aides -- a move that might trigger some departures.

At his announcement, Kerry was joined by crew members of a Navy gunboat he commanded in Vietnam, where he won a Silver Star, Bronze Star and three Purple Hearts. Introducing Kerry was former Sen. Max Cleland of Georgia, who lost both legs and an arm in Vietnam combat. It is all part of Kerry's core argument that his military experience gives him unique credibility among the nine Democratic contenders to confront Bush on national security issues.

Shortly after the speech, Kerry embarked on a three-state swing that took him to Iowa, and ends Wednesday with appearances in New Hampshire and at Boston's famed Faneuil Hall.

Months ago, Kerry made clear his intention to seek the party's nomination, and he attracted a great deal of attention from the Democratic establishment. John Forbes Kerry has the initials of a one-time Democratic president -- JFK -- and a comparable pedigree -- Ivy League education, commander of a small Navy craft during wartime and Massachusetts senator.

Last October, he voted for the congressional resolution authorizing Bush to use military force in Iraq, but he has been sharply critical of the president's diplomatic efforts. He stirred controversy earlier this year when he said the United States needed a "regime change."

Kerry sketched out no new proposals in his announcement, but sought to put the focus on broad themes he hopes to sound in the campaign.

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AP Political Writer Ron Fournier in Washington contributed to this report.