WASHINGTON -- Republican challenger Mitt Romney's campaign strove to turn the page on a week of public stumbles Sunday, promising a redoubled effort in the most competitive states to undercut President Barack Obama's economic record as voters tune in for the final six weeks of a close race.

Obama, taking a rare break from the campaigning ahead of an address to world leaders at the U.N. General Assembly on Tuesday, dispatched top allies to try to keep Romney's missteps alive in the minds of a dwindling cadre of undecided voters.

With about six weeks remaining before the Nov. 6 election, the handful of so-called swing or battleground states appear likely to determine the outcome of what has been an extremely close contest between Obama and Romney. Those states become even more critical to the Republican candidate as recent polling shows Obama opening a lead in many of them.

The U.S. president is not chosen by the nationwide popular vote but in state-by-state contests. While most states reliably vote for the candidate of one party or the other, the eight or so swing states are seen as toss-ups.

Polls show Obama in a near tie with Romney nationally. But a new Wall Street Journal/NBC News/Marist Poll shows the president with leads among likely voters of 8 percentage points in Iowa and 5 points each in Colorado and Wisconsin, all battleground states. Polls published earlier this week pointed to leads for Obama in Virginia and Ohio. While he and Romney are neck-and-neck in North Carolina, Obama has an edge in Florida and New Hampshire.

With those factors pressing hard on Romney, he is intensifying his swing-state campaigning to counter criticism from Republican heavyweights that his bid for the nation's highest office is mismanaged and misdirected.

"The Romney campaign has to get turned around. This week I called it incompetent, but only because I was being polite. I really meant 'rolling calamity,"' Wall Street Journal columnist Peggy Noonan, a former speechwriter for President Ronald Reagan, wrote late last week.

A Romney rally scheduled for Sunday evening at a Denver-area high school represents his first public event of the weekend. As the November vote draws near, he also is facing pressure to spend less time raising money and more time explaining his plans to voters in swing states.

The schedule shift comes in the last full week before the presidential debates move the campaign into a new phase -- one which Romney advisers suggest could prove pivotal following several weeks marked by negative attention, missteps and Republican concerns.

Both candidates were looking ahead to the pivotal next phase of the campaign, where the three presidential debates -- the first on Oct. 3 in Denver -- present the greatest opportunities to speak directly to voters or to get tripped up by a gaffe-turned-sound bite with little time to recover before Election Day.

Rehearsal for those debates consumed the early part of the day for the former Massachusetts governor, who huddled with senior advisers in Los Angeles ahead of his Denver-area rally. Romney has consistently taken time from his campaign schedule in recent weeks to focus on debate preparation -- whether studying up on policy issues or roleplaying with Ohio Sen. Rob Portman, who has been tapped to play Obama in Romney's debate dry runs.

While both sides are downplaying expectations, Romney's campaign sees the debates -- the first one in particular -- as a huge opportunity to get his campaign and its message back on track after a troublesome week. A secretly recorded video released Monday showed Romney at a Florida fundraising event writing off his prospects for winning over the almost half of Americans who he said pay no federal income taxes, are dependent upon government help and see themselves as victims dominated the week.

"That certainly was a political analysis at a fundraiser, but it's not a governing philosophy," Republican Sen. Kelly Ayotte of New Hampshire, a prominent Romney supporter, said on NBC television's "Meet the Press." "He absolutely has a vision for 100 per cent of America. And that is really different from this president."

But even many conservatives were publicly sweating over the remarks, which seemed to play into Democrats' caricature of Romney as an out-of-touch plutocrat. Also dogging Romney were reports of internal finger-pointing within his campaign and questions about his foreign policy judgment.

Addressing donors Saturday night in Democrat-friendly California, Romney sought to translate the scuffle over the video into a policy debate about the growth of government under Obama's leadership.

"This is a tough time. These are our brothers and sisters. These are not statistics. These are people," Romney declared. "The president's policies -- these big-government, big-tax monolithic policies -- are not working."

In an interview set to air Sunday night, Romney told CBS television his campaign is moving in the right direction.

"It doesn't need a turnaround. We've got a campaign which is tied with an incumbent president to the United States," Romney says, according to remarks released in advance by CBS.

Hoping to discharge another long-problematic issue during an already lost week, Romney on Friday released his 2011 tax returns showing income of $13.7 million, largely from investments. He paid federal income tax at a 14.1 per cent rate, lower than that of most middle-income Americans.

Citing Romney's refusal to release more than two years of returns, Obama aides argued that wasn't enough, seeking to parlay the issue into a broader condemnation of Romney's reluctance to lay out the specifics about how his tax plan would affect average Americans.

"He's not been straight with the American people about his taxes," said Obama campaign adviser Robert Gibbs. "He's not been straight with the middle-class people, families, in this country about what is going to happen to their taxes."

Romney spent much of his weekend in high-dollar fundraisers in southern California, a state that has gone Democratic in the last five presidential elections.

But he now is refocusing his schedule to visit more frequently the most competitive states. Romney adviser Kevin Madden defended the fundraising focus as a necessity, but said that intensity would be matched by an aggressive schedule of public events starting Sunday.

From Denver, Romney was to begin a three-day bus tour in Ohio on Monday followed by a stop in Virginia -- states that Obama won in 2008 but that Republicans claimed four years earlier. Obama, meanwhile, was set to be in New York on Monday and Tuesday for a speech before the United Nations General Assembly, plus an appearance on ABC's morning TV show "The View."