WASHINGTON • President Barack Obama bypassed Congress this past week by appointing Dr. Donald Berwick, a health policy expert, to run Medicare and Medicaid, saying he was needed to carry out the new health care law, which calls for huge changes in the two programs that together insure nearly one-third of all Americans.

Dan Pfeiffer, the White House communications director, said the president decided to act because "many Republicans in Congress have made it clear in recent weeks that they were going to stall the nomination as long as they could, solely to score political points," Pfeiffer said.

As a recess appointee, Berwick has all the powers of a permanent appointee. But under the Constitution, his appointment will expire at the end of the next session of Congress, in late 2011.

In April, Obama nominated Berwick to be administrator of the Centers for Medicare and Medicaid Services. The agency has been without a permanent administrator since October 2006.

The recess appointment was somewhat unusual because the Senate is in recess for less than two weeks and senators were still waiting for Berwick to submit responses to some of their requests for information. No confirmation hearing has been held or scheduled.

Although hospital executives who have worked with Berwick describe him as a visionary, inspiring leader, he would have faced a long, difficult struggle to win Senate confirmation.

The president's action gives the administration a strong voice to defend provisions of the new law that have come under almost daily attack from Republicans in Congress and in political campaigns around the country.

Berwick, a pediatrician, is president and co-founder of the Institute for Healthcare Improvement, a nonprofit organization in Cambridge, Mass. He is also a professor at Harvard Medical School and the Harvard School of Public Health.

Republicans have used the nomination to revive their arguments against the new health care law, which they see as a potent issue in this fall's elections.

In two decades as a professor of health policy and as a prolific writer, Berwick has championed the interests of patients and consumers. At the same time, he has spoken of the need to ration health care and cap spending, has supported efforts to "reduce the total supply of high-technology medical and surgical care" and has expressed great admiration for the British health care system.

Under the new law, Medicare will be a testing ground for many innovations that reward high-quality care and penalize providers of poor care. The law will expand Medicaid to cover 16 million more people with low incomes.

Sen. Pat Roberts, R-Kan., said that, far from trying to delay a confirmation hearing, Republicans had wanted a forum where Berwick could explain his views.

"This recess appointment proves the Obama administration did not have the support of a majority of Democrats and Republicans in the Senate and sought to evade a hearing," Roberts said.

But Ronald F. Pollack, executive director of Families USA, a liberal-leaning consumer group, welcomed the appointment, saying "it augurs well for the implementation of health care reform."

One of Berwick's first tasks will be to work with Congress to avert a 21 percent cut in Medicare payments to doctors, scheduled to occur late this year.

The American Medical Association has praised Berwick, saying he is "widely known and respected" for his efforts to improve the quality and safety of care. But cuts in Medicare payments could damage the quality of care and prompt doctors to turn away new Medicare patients, doctors say.