President Obama has left no doubt that he will make a sharp break with the policies of his predecessor, President George W. Bush. But after just one day in office, it is clear that Mr. Obama’s break will be one of style, as well as substance.

An air of informality surrounds the Obama White House that might leave Bush advisers aghast. On Wednesday morning, Mr. Obama was seen in the Oval Office without a suit jacket – a definite no-no in the Bush administration. Even more striking was the new president’s demeanor as he signed executive orders Thursday to shut down the prison at Guantanamo Bay, Cuba and to reverse other Bush anti-terror policies.

In the Bush White House, presidential appearances were short and to the point. When the president was done speaking, junior aides would call out “Thank you!” – a signal to reporters and photographers that it was time to leave the room. On Thursday, Obama aides did the same. “Thank you!” one called, after the president signed the first executive order.

But a reporter shouted, “No, there’s another one!” Mr. Obama chimed in. “There are three of these,’’ he said.

Then, instead of reading from a script, as Mr. Bush might have done, the new president winged it, offering off-the-top-of-his head explanations for each of his actions before putting down his signature. Several times, he double-checked his facts with his White House counsel, Gregory B. Craig.

“Is that correct, Greg?’’ Mr. Obama asked. All the while, the television cameras rolled.