COLUMBUS, Ohio (AP) ― President Barack Obama plunged into his campaign for a new term and tore into rival Mitt Romney on Saturday as a willing and eager “rubber stamp’’ for conservative Republicans in Congress who want to cut taxes for the rich.

Six months before Election Day, the polls point to a close race between Obama and Romney, with the economy the overriding issue as the U.S. struggles to recover from the worst recession since the 1930s. Unemployment remains stubbornly high at 8.1 percent nationally, although it has receded slowly and unevenly since peaking several months into the president’s term. The most recent dip was due to discouraged jobless giving up their search for work.

Romney has staked his candidacy on an understanding of the economy, developed through a successful career as a businessman, and his promise to enact policies that stimulate job creation. But Obama said his rival was merely doing the bidding of the conservative powerbrokers in Congress and has little understanding of the struggles of average Americans.

Romney and his “friends in Congress think the same bad ideas will lead to a different result, or they’re just hoping you won’t remember what happened the last time you tried it their way,” the president told an audience estimated at over 10,000 supporters at Ohio State University in Columbus. Aides insisted it was his first full-fledged political rally of the election year.

Romney “doesn’t seem to understand that maximizing profits by whatever means necessary, whether it’s through layoffs or outsourcing or tax avoidance, union busting, might not always be good for the average American or for the American economy,” the president said.

“Why else would he want to cut his own taxes while raising them for 18 million Americans,” Obama said of his multimillionaire opponent.

While Romney has yet to flesh out a detailed economic program, he and Republicans in Congress want to extend all the tax cuts enacted during President George W. Bush’s administration that are due to expire at year’s end. Obama and most Democrats want to let taxes rise for upper-income earners.

The president’s campaign chose Ohio State University and Virginia Commonwealth University for the back-to-back rallies. Obama won both states in his successful race in 2008, although both have elected Republican governors since, and are expected to be hotly contested in the fall.

Obama has attended numerous fundraisers this election year, but over the escalating protests of Republicans, the White House has categorized all of his other appearances so far as part of his official presidential duties.

The staging of Saturday’s events eliminated any doubt about his purpose. Official campaign rallies can free Obama up to take more direct aim at Romney.

He was introduced in Columbus and again in Richmond by first lady Michelle Obama, and walked in to the cheers of thousands, many of them waving campaign-provided placards that read “Forward.”

While the president is notably grayer than he was four years ago, he and his campaign worked to rekindle the energy and excitement among students and other voters who propelled him to the presidency in 2008.

“When people ask you what this election is about, you tell them it is still about hope. You tell them it is still about change,” he said. It was a rebuttal to Romney’s campaign, which has lately taken to mocking Obama’s 2008 campaign mantra as “hype and blame.”

If the economy is a potential ally for Romney, Obama holds other assets six months before the vote.

Unlike Romney, who struggled through a highly competitive primary season before recently wrapping up the nomination, Obama was unchallenged within his own party. As a result, his campaign’s most recent filing showed cash on hand of $104 million, compared with a little over $10 million for Romney. His campaign has worked to build organizations in key states for months.

But in the aftermath of recent Supreme Court rulings, modern presidential campaigns are more than ever waged on several fronts, and the effect of super political action committees and other outside groups able to raise donations in unlimited amounts is yet to be felt.

Already, while Romney pauses to refill his coffers, the super PAC Restore Our Future has spent more than $4 million on television advertising to introduce the Republican candidate to the voters.

Romney had no public events Saturday after spending much of the week campaigning in Virginia and Pennsylvania.

A campaign spokeswoman, Andrea Saul, responding to Obama’s speech in Ohio, said, “While President Obama all but ignored his record over 3 1/2 years in office, the American people won’t. This November, they will hold him accountable for his broken promises and ineffective leadership.’’

With his rhetoric, Obama belittled Romney and signaled he intends to campaign both against his challenger and the congressional Republicans who have opposed most of his signature legislation overwhelmingly, if not unanimously. Polls put the Congressional job approval rating in the low teens.

After a spirited campaign for the Republican nomination, Obama said, the Republican leadership picked someone “who has promised to rubber stamp’’ their agenda if he gets a chance. He said the Republican agenda includes more tax cuts for rich Americans, spending reductions for education and health care, and enhancing the power that big bands and insurers hold over consumers.

Scarcely more than a dozen states figure to be seriously contested in the fall, including the two where Obama was campaigning Saturday.

They include much of the nation’s industrial belt, from Wisconsin to Michigan, Ohio and Pennsylvania, as well as Nevada, Colorado and, the president’s campaign insists, Arizona; the latter three all have large Hispanic populations. Both campaigns also are focusing on Iowa, Florida, North Carolina, Virginia and New Hampshire. Together, those states account for 157 electoral votes.

Electoral votes are allotted based on the number of seats each state has in both chambers of Congress. Seats in the House of Representatives are based on population, while each state has two senators. State-by-state contests award the 270 electoral votes needed to win the election.

Barring a sudden crisis, foreign policy is expected to account for less voter interest than in any presidential campaign since the attacks of Sept. 11, 2001. Since taking office, Obama has made good on his pledge to end the war in Iraq, announced a timetable to phase out the U.S. combat role in Afghanistan by 2014 and given the order for a risky mission by special forces in which al-Qaida leader Osama bin Laden was killed in his hideout in Pakistan.