Under Mr. Bush, punctuality was a virtue. Meetings started early  the former president once locked Secretary of State Colin L. Powell out of the Cabinet Room when Mr. Powell showed up a few minutes late  and ended on time. In the Obama White House, meetings start on time and often finish late.

When the president invited Congressional leaders to 1600 Pennsylvania Avenue last week to talk about his economic stimulus package, the session ran so long that Mr. Obama wound up apologizing to the lawmakers  even as he kept them talking, engaging them in the details of the legislation far more than was customary for Mr. Bush.

“He was concerned that he was keeping us,” said Representative Eric Cantor of Virginia, the Republican whip. “He said, ‘I know we need to get you all out of here at a certain time.’ But we continued the discussion. What are you going to say? It’s the president.”

If Mr. Obama’s clock is looser than Mr. Bush’s, so too are his sartorial standards. Over the weekend, Mr. Obama’s first in office, his aides did not quite know how to dress. Some showed up in the West Wing in jeans (another no-no under Mr. Bush), some in coats and ties.

So the president issued an informal edict for “business casual” on weekends  and set his own example. He showed up Saturday for a briefing with his chief economic adviser, Lawrence H. Summers, dressed in slacks and a gray sweater over a white buttoned-down shirt. Workers from the Bush White House are shocked.

“I’ll never forget going to work on a Saturday morning, getting called down to the Oval Office because there was something he was mad about,” said Dan Bartlett, who was counselor to Mr. Bush. “I had on khakis and a buttoned-down shirt, and I had to stand by the door and get chewed out for about 15 minutes. He wouldn’t even let me cross the threshold.”

Image In a visit to the Capitol on Tuesday, Mr. Obama surprised his former Senate colleagues by stopping to talk to reporters. Credit... Ruth Fremson/The New York Times

Mr. Obama has also brought a more relaxed sensibility to his public appearances. David Gergen, an adviser to both Republican and Democratic presidents, said Mr. Obama seemed to exude an “Aloha Zen,” a kind of comfortable calm that, Mr. Gergen said, reflects a man who “seems easy going, not so full of himself.”