Doug Mills/The New York Times

President Obama will challenge Republican foes of the newly created Consumer Financial Protection Bureau by naming Richard Cordray as its director while Congress is out of town.

Philip Scott Andrews/The New York Times

That would allow the agency to establish new regulations over financial institutions, putting into effect elements of the financial regulatory overhaul that was one of the administration’s main achievements in Congress.

Mr. Obama’s exercise of constitutional powers to name top officials without Senate confirmation while Congress is in recess is a stiff challenge to Republicans, who have attempted to block the maneuver by holding “pro forma” sessions over the holidays.

Senator Mitch McConnell of Kentucky, the Republican leader, objected strenuously, saying Mr. Obama was overstepping the bounds of his executive power and leaving the agency open to legal challenges.

“Although the Senate is not in recess, President Obama, in an unprecedented move, has arrogantly circumvented the American people,” he said in a statement.

Mr. Cordray accompanied the president on Wednesday on a trip to Ohio, where the president is expected to deliver remarks on the economy at a high school in the Cleveland suburb of Shaker Heights. Cleveland is Mr. Cordray’s hometown.

Mr. Cordray looked a little shell-shocked when he got off Marine One to board Air Force One for the flight to Cleveland, clutching his brown folder to his chest as he walked to the plane.

But he sounded ready for battle once the plane landed in Cleveland and reporters cornered him under the wing, issuing a not-so-veiled warning to Wall Street.

“We’re going to begin working to expand our program to non-banks, which is an area we haven’t been able to touch before now,” he said.

The recess appointment represents a sharp departure from a long-standing precedent that has limited the president to recess appointments only when the Senate is in a recess of 10 days or longer. Breaking from this precedent lands this appointee in uncertain legal territory, threatens the confirmation process and fundamentally endangers the Congress’s role in providing a check on the excesses of the executive branch.

Jay Carney, the White House press secretary, called the recess appointment a “no-brainer,” and said that Mr. Obama would not be waiting around for Congress to act this year.

“He nominated Richard Cordray six months ago,” Mr. Carney said. “He won a majority of support in the Senate, yet Republicans refused to allow an up-or-down vote. This is a shame.”

He declined to speak about the legal and constitutional challenge which may be ahead, but said White House lawyers were confident. “When pro forma sessions are simply used as an attempt to stop the president from making an appointment,” then Mr. Obama was within his rights to move ahead.

President Bush, by this point in his tenure, Mr. Carney noted, had made 61 recess appointments, compared to Mr. Obama’s 28.

Senator Tim Johnson, a Democrat of South Dakota who is chairman of the Banking Committee, praised Mr. Cordray’s appointment.

“Mr. Cordray is eminently qualified for the job, as even my Senate Republican colleagues have acknowledged,” he said. “It’s disappointing that Senate Republicans denied him an up-or-down vote, especially when it’s clear he had the support of a majority of the Senate.”

The move came hours after the conclusion of the Iowa caucuses, and was sure to turn attention away from the Republican Party and back to the president.

In December, Mr. Cordray’s nomination was rejected after Democrats failed to achieve the 60 votes they needed to move his nomination forward.

The power struggle between the financial sector and its check-cashing, card-carrying customers has developed into one of the fault lines along which the political parties are playing out their own rivalries as the election year arrives.

Mr. Cordray is a former attorney general of Ohio noted for his aggressive investigations of mortgage foreclosure practices. Currently in charge of enforcement at the consumer agency, he was nominated in July to lead it.

Previous opposition from Republicans led to the withdrawal of Elizabeth Warren from consideration for the post. She is a Harvard law professor who was the driving force behind the agency’s creation and is now a Democratic candidate for the United States Senate in Massachusetts.