WASHINGTON  President Obama has taken full control of the health care negotiations, casting himself for the first time in the role of mediator between the House and Senate during a 72-hour marathon of talks that have turned his White House into a de facto Congressional conference.

Mr. Obama spent more than six hours with Democratic leaders on Wednesday, slipping in and out of health care talks to coordinate a response to the earthquake in Haiti. He spent much of Thursday in health care talks, ducking out in the evening to address House Democrats and attend his daughter Malia’s band recital (she plays flute) and then returning to the negotiating table until 1 a.m., shortly before the group recessed for the night.

He was back at it Friday afternoon, holed up once again in the Cabinet Room from 1 p.m. to 3:45 p.m., at which point the White House announced that Mr. Obama was done holding or attending health care meetings, at least for now  a signal that officials are waiting for cost analysis from the Congressional Budget Office.

“It was always our sense that once the bills were passed that he would have to play a much more direct role in helping work out the details,” his senior adviser, David Axelrod, said in an interview, as the talks went on down the hall from his West Wing office. “This has been a prodigious task from start to finish; we knew it would be.”