During an appearance at the Conservative Political Action Conference, Hatch was asked why conservatives should believe him when he discusses federal spending, given his vote in favor of the bailout. That vote has become a litmus test for conservatives and anathema for Republicans running for re-election.
"All I can say is, there aren't many people who will say I'm sorry. I'm one who will," said Hatch, who earlier this week met with tea party activists at a town hall-style meeting.
Hatch is looking for support from his party's conservative base for a re-election bid next year. The 76-year-old will not have it from his fellow Utah senator; Sen. Mike Lee said Friday he won't endorse Hatch.
Tea party activists in Utah sent Republican Sen. Bob Bennett packing for working across party lines on an alternative to the health overhaul legislation that Democrats championed. Bennett did not get the party's nomination in the party purity test with Lee.
Defending his vote and apologizing for it as well, Hatch said he listened to President George W. Bush and his treasury secretary, Henry Paulson, when they strongly urged Congress to act.
"You may disagree, but you're not sitting there having to make these decisions. I probably made a mistake voting for it," Hatch said.
The angry reaction from the crowd drew a scolding from the panel's moderator.
"I've fought in the trenches with this man," said Lew Uhler of the National Tax Limitation Committee. "Nobody is more committed to conservative principles than this man - Orrin Hatch, the senior senator from Utah."
Hatch said he did what he thought was best.
"At the time, we were in real trouble and it looked like we were ready for a depression," he said. "I believe we would have gone into a depression."
Conservatives a day earlier heckled Vice President Dick Cheney when he made a surprise appearance, calling him a "draft dodger" and "war criminal." The gathering of more than 11,000 people is packed with conservatives key to those seeking the GOP presidential nomination.