CANNON FALLS, Minn. — Hitting back against an emboldened GOP, President Barack Obama launched a rare direct attack Monday on the Republican presidential field, criticizing his potential 2012 rivals for their blanket opposition to any deficit-cutting compromise involving new taxes.

“That’s just not common sense,” Obama told the crowd at a town hall-style meeting in Cannon Falls, Minn., as he kicked off a three-day bus tour through Minnesota, Iowa and Illinois.

“You need to take a balanced approach,” he insisted.

Obama recalled a moment in last week’s GOP presidential debate when all eight of the candidates said they would refuse to support a deal with tax increases, even if tax revenues were outweighed 10-to-1 by spending cuts.

Obama didn’t mention any of the candidates by name, and prefaced the remark by saying, “I know it’s not election season yet.”

But his comment underscored that election season is indeed under way. The bus tour, although an official White House event rather than a campaign swing, takes Obama through three states he won in 2008 but where he now needs to shore up his standing.

In Iowa, Obama returns to a state that handed him a key victory over Democratic rival Hillary Rodham Clinton in their nomination fight but where Republicans have now been blanketing the state in preparation for its first-in-the-nation caucuses, attacking the president at every turn. The bus tour comes on the heels of Republican Michele Bachmann’s weekend victory in the Iowa Straw Poll and Texas Gov. Rick Perry’s contest-rattling entrance into the race.

It also comes after the president spent much of the summer holed up in the nation’s capital enmeshed in bitter, partisan negotiations on the debt crisis that cratered his approval ratings and those of Congress amid a faltering economy and high unemployment.

Later in the town-hall meeting, Obama got a question on his signature health care law, and took a hard shot at Mitt Romney, a GOP front-runner who has had to defend implementing a health care plan while governor of Massachusetts that’s similar to the federal version.

“You’ve got a governor who’s running for president right now who instituted the exact same thing in Massachusetts,” Obama said, referring to a central component of his law — the requirement for nearly everyone to carry health insurance.

“This used to be a Republican idea,” Obama said. “It’s like suddenly they got amnesia.”

The so-called individual mandate in Obama’s health care law was struck down by a federal appeals court last week but Obama expressed confidence that the Supreme Court ultimately would uphold it if justices follow existing law and precedent. If not, he said, “we’ll have to manage that when it happens.”

In response to a question, Obama also took the chance to counter the anti-government stance embraced by the tea party and largely by the Republican presidential field.

He noted that although government doesn’t do everything well, it is responsible for sending a man to the moon and for the military defending the country, among other things.

“When you go to the National Parks and those folks in the hats, that’s government,” Obama said.

“As frustrated as you are about politics don’t buy into this notion that somehow government is what’s holding us back,” he said.

Eager to get out of Washington, Obama struck a casual tone as he spoke to a crowd gathered in a picturesque park on the banks of the Cannon River, ditching his suit and tie for rolled-up sleeves and khakis for the open-air event.

Despite the widespread frustration with Washington documented in national polls, the president got a rosy reception.

Some of his questioners never even bothered to ask him questions, and the president used the format to offer broad, if sometimes wonkish, explanations of his agenda.

People asked him about education, health care, broadband cable and the cost of prescription drugs. One woman told him she was recovering from lung cancer and had slept in her truck for two days to ask him a question about Social Security, although the president missed the chance to sympathize with her about her health when he responded with a defense of Social Security.

The woman, Lois Dare, 53, expressed disappointment later that Obama didn’t acknowledge her situation.

“I need help,” she said. “I was hoping he would have said, ‘Let me take some information down and go back to the White House’.”

Dare still has hope. She passed a note to an Obama handler reiterating her plea.

Obama began his remarks at the town hall with what’s becoming a refrain: criticizing Congress, accusing lawmakers of putting politics ahead of the country and calling on voters to tell them to cut it out.

“You’ve got to send a message to Washington that it’s time for the games to stop, it’s time to put country first,” Obama said.

“I want everyone to understand here, I’m not here just to enjoy the nice weather; I’m here to enlist you in a fight,” he said. “We are fighting for the future of our country. And that is a fight that we are gonna win. That is a promise that I make, with your help.”

Appearing in Cannon Falls ahead of Obama’s town hall, Republican National Committee chairman Reince Priebus rallied a few dozen tea party members and College Republicans.

“We won’t stand idly by while he uses our hard-earned tax dollars to spin his failure to put America back to work,” Priebus said.

After his event in Cannon Falls, Obama got back in his black, unmarked bus to drive south into Iowa where he was holding another town hall Monday afternoon in Decorah. En route he made an unscheduled stop for lunch at the Old Market Deli in Cannon Falls with five Minnesota military veterans who served after the Sept. 11, 2001 terror attacks.

On Tuesday the president holds what the White House is billing as a “rural economic forum” in Peosta, Iowa, near the Illinois border, where he’ll be joined by Agriculture Secretary Tom Vilsack to announce several initiatives for rural areas. He’ll wrap up Wednesday with town halls in Atkinson in northwestern Illinois, and then in nearby Alpha, Ill., before returning to Washington. On Thursday he flies with his family to Martha’s Vineyard in Massachusetts for his annual summer vacation.