President Obama’s reelection campaign, facing an onslaught of attack ads from well-funded conservative interest groups, is concentrating its television advertising in fewer states than in his 2008 presidential bid, a review of campaign spending shows.

Unlike in his first campaign, when Obama held a significant financial advantage over Republican John McCain, his resources in the current contest are more evenly matched with those of Mitt Romney, the GOP candidate. That is in large part because of the spending by independent interest groups, which favor Republicans.

Obama’s campaign has placed ads in fewer than 60 media markets nationwide, skipping some expensive areas such as Philadelphia and Washington, compared with 80 in the early weeks of the 2008 general-election campaign. In 2008, Obama began running ads against McCain in late June.

The president’s campaign has put an increased focus on Ohio, which has become the most competitive big prize in the race. Four of the most saturated media markets for presidential advertising are in Ohio, and Obama’s campaign has spent more on broadcast advertising there than in Florida, another critical swing state with about twice the population.

That is in contrast to Obama’s spending in the opening weeks of 2008, when Florida received nearly twice as much advertising money as Ohio, according to estimates of spending from Kantar Media/CMAG.

“They can win without Ohio, but if they win Ohio they will be reelected,” said Jim Jordan, a Democratic strategist. He and others say that if Obama could repeat his 2008 victory in Ohio, he would need to secure just two or three of the other roughly half-dozen most competitive swing states. “There’s just no way Romney can win without flipping Ohio,” Jordan said.

Obama campaign officials said they have not emphasized television advertising, choosing instead to focus on face-to-face interactions with voters.

“We believe that being on the ground in communities all across the country is where the real conversations about the choice in this election happen,” said Katie Hogan, a campaign spokeswoman. “This campaign set out to expand the map in 2011, making as many routes to victory as possible.”

The campaign also has made Ohio the biggest target of an expanded voter-mobilization effort, opening 25 field offices in the state, funded with most of the $2.6 million transferred to the Ohio state party, more funding than any other part of the country has received.

By comparison, Romney is far behind Obama when it comes to field offices and the other infrastructure needed to make voter contacts. Obama and the Democratic Party have four times as many staff members around the country as Romney and the Republicans, according to a Washington Post analysis of campaign spending reports through April 30, the latest information available.

Romney spokeswoman Andrea Saul dismissed the importance of the Obama team’s larger field operation, saying, “No matter how many hundreds of field offices and campaign staffers they have, it won’t make up for the 23 million Americans who are struggling for work.”

Strategists say the Obama campaign’s focus on Ohio is a tacit admission that it may be easier for the president to win than the biggest swing state, Florida.

In Florida, ad spending by the campaign is targeted: More than a third of the spending has been in the Orlando market, reaching the greatest concentration of swing voters along the I-4 corridor. Four years ago, 1 in 6 television dollars was spent in Orlando.

Spending in a handful of smaller states — Colorado, Iowa, Nevada and Virginia — reflects a second tier of battle. Nevada alone, with only six electoral votes, has received $2.2 million in advertising money from Obama.

In Wisconsin, the Obama campaign has focused on face-to-face voter contact ahead of Tuesday’s election to recall Gov. Scott Walker (R), leaving the airwaves to state candidates. The outcome of the effort will determine how much the two presidential campaigns focus on the state before November, strategists say.

Polls suggest that North Carolina may be tough for Obama to win this year, but his campaign has not pulled back on its investment there. The state, which will host the Democratic National Convention just after Labor Day, has brought in $2.3 million in ad spending from the Obama campaign, the largest share after Ohio and Florida.

“It’s hard for them to pull out of North Carolina,” said Ken Goldstein, who tracks political ad spending as president of Kantar Media/CMAG, “but at some point they’re going to have to make a hardheaded decision.”

The Obama campaign has made a very limited investment in Arizona, although campaign officials said they would like to see the traditionally red state become a battleground. The campaign has bought no television time there and has opened five offices, compared with a dozen or more in neighboring Nevada, which has half the population. The Arizona Democratic Party has received just $322,000 from the Democratic National Committee.

Romney’s campaign has been able to save money on television ads because Republican interest groups have spent millions attacking Obama on his behalf. His campaign is running ads in six states, but, like Obama’s, is concentrating on Ohio, spending 1 in 3 ad dollars there.

Some Republicans point to Obama’s poor showing in Democratic primaries in the coal states of West Virginia and Kentucky, saying that could spell trouble for him in southeastern Ohio.

“People that are upset don’t stop at borders,” said Bob Bennett, the Ohio Republican Party chairman.

Only a small portion of Ohio’s population lives in that part of the state, however.

In 2008, Obama won the state in large part by turning out minority voters and winning over suburbanites around major cities. That year, he was the first Democrat to win the Columbus media market since Lyndon B. Johnson in 1964, said Mike Dawson, a Republican and Ohio elections expert. Obama formally launched his campaign in Columbus last month, highlighting the region’s importance.

“The key is going to be the Columbus media market,” Dawson said, adding that “it was such an aberration.”