While Mr. Geithner nodded vigorously in approval as he stood in the Rose Garden with Mr. Obama and Ms. Warren, his dealings with her have been the subject of much speculation. Ms. Warren, as the chairwoman of the Congressional panel that oversees the Troubled Asset Relief Program, has often been critical of Mr. Geithner and his department for the management of the financial rescue program. Privately, Mr. Geithner promoted Mr. Barr for the consumer post.

Under the financial regulation law, Treasury will have the powers delegated to the bureau until a permanent director is nominated and confirmed by the Senate to a five-year term. Next July the bureau will assume the regulatory power for consumer rights now vested in a range of agencies, including the Federal Reserve, the Federal Trade Commission, the Federal Deposit Insurance Corporation and the Department of Housing and Urban Development, which have been widely criticized for not making consumer protection a priority.

Once a director is confirmed, the bureau can issue regulations and enforce new standards for mortgages, credit cards, payday loans and a wide array of other financial products.

It is expected to have a budget of up to $500 million and hundreds of employees, many of them drawn from the agencies that will give up responsibilities for consumer protection. The bureau will nominally be part of the Fed, which is obligated to finance its budget, but its personnel and rule-making decisions are to be made independent of the central bank.

Ms. Warren, 61, an authority on bankruptcy law, developed her following among liberals with her writings and advocacy on behalf of working-class families. But she has drawn fire from financial institutions for her persistent attacks on abusive, deceptive and unfair lending practices. Banking executives as well as some Treasury officials say she has been overly broad in criticizing those practices, and showed some misunderstanding of financial markets.

Republicans were quick to criticize Mr. Obama for circumventing a Senate confirmation. Senator John Thune of South Dakota, the chairman of the Republican Policy Committee in the Senate, said in a statement, “This appointment lacks transparency and represents the latest power grab by the president to expand the reach of an intrusive government into the lives of Americans.”

Ms. Warren, writing on the White House Web site, said, “The new law creates a chance to put a tough cop on the beat and provide real accountability and oversight of the consumer credit market. The time for hiding tricks and traps in the fine print is over.”