COLUMBIA, S.C. — Facing attacks on his character from some particularly aggressive and well-financed opponents, President Obama will begin running the first broadcast television ad of his presidential re-election campaign on Thursday.

To advertise so early in an election year is unusual. But it reflects the new reality of presidential politics, with large, anonymous amounts of money flowing into groups that can pay for potentially devastating advertising.

The president’s campaign commercial is striking not only for its timing but for its sharply defensive tone toward a very specific target. Without mentioning them by name, it takes on Charles and David Koch, the wealthy conservative businessmen who have opposed Mr. Obama through the political advocacy group Americans for Prosperity.

Americans for Prosperity announced this week that it would run a $6 million national advertising campaign that portrays the president as running a pay-to-play government. It attacks him in a commercial that highlights the Solyndra scandal, which involved a solar power company with ties to the Obama administration that declared bankruptcy after receiving more than $500 million in federal money.

The Obama campaign responded hastily. It placed orders for television time on Wednesday, telling broadcast stations that it wanted the advertising on the air immediately. Typically, stations require more than a day’s notice.

An official from the campaign said that the purchase of air time was significant, but as of Wednesday afternoon it had not placed orders widely, according to several television stations in battleground states.

The ad will run in four states that could prove pivotal in the election: Michigan , North Carolina , Ohio and Virginia .

It opens with a shot at the Koch brothers. “Secretive oil billionaires attacking President Obama with ads fact checkers say are not tethered to the facts,” an announcer says over the low chords of a piano as an image from the Americans for Prosperity advertisement plays in the background. “Independent watchdogs call this president’s record on ethics unprecedented,” it continues. “President Obama kept his promise to toughen ethics rules and strengthen America’s energy economy.”

Groups like Americans for Prosperity and American Crossroads have been airing advertising for months attacking the president, to the tune of tens of millions of dollars. This is the first time he has pushed back in a commercial.

The ad coincides with what promises to be a major media blitz next week for the president. He is set to deliver his State of the Union speech on Tuesday. Then he will hit the road, traveling to Arizona , Colorado , Iowa , Michigan and Nevada — all swing states his campaign is focusing on in the election.

That the ad came directly from the Obama campaign — and not from a “super PAC” supporting him — could indicate how differently the Republican and Democratic sides of the race will unfold. Attack ads in the Republican primary so far have been paid for overwhelmingly by super PACs. But the president — who recently announced that he had raised $68 million in the last three months of 2011 — is likely to have to do much of the hard hitting himself. His super PAC has so far failed to raise the amounts of money of its Republican counterparts.