The shift came on the heels of accusations by presumed Democratic presidential nominee John Kerry that the president was "stonewalling" investigations of the terrorist attacks and U.S. intelligence failures.
"It appears he doesn't want to let the facts get in the way of his campaign," presidential spokesman Scott McClellan said of Kerry.
The White House had insisted on the hour time limit but Tuesday, spokesman Scott McClellan said, "the President will answer all of the questions they want to raise," reports CBS News Correspondent Peter Maer.
"This administration has provided unprecedented cooperation to the 9/11 commission," McClellan said. "It provided access to every single bit of information that they have requested."
It was the administration's second change of heart about the commission. Mr. Bush originally had opposed the panel's request for a two-month extension of its work but he eventually relented.
The 10-member commission sought interviews with President Bush and Vice President Dick Cheney about what the administration knew before the attacks, potentially a sensitive subject in an election year.
The president had agreed to meet privately for an hour with the chairman and vice chairman of the commission, but said it was unnecessary for him to testify publicly. Cheney also has said he would meet with some commissioners.
Commission members are seeking public testimony from Bush's national security adviser, Condoleezza Rice, who has refused to appear on the advice of White House lawyers. Rice has testified in private before the commission and, McClellan said, "only five members showed up."
In previous hearings, the commission has highlighted government missteps before the 2001 attacks, including miscommunications about al Qaeda operatives dating back to the mid-1990s and hijackers who were allowed to enter the United States repeatedly despite lacking proper visa documentation. Up to now, however, the panel has not assigned blame beyond midlevel officials in federal agencies.