"Without a doubt; 100 percent," Gaudin said.
Harden was dominant Tuesday in his final Minor League tuneup before his expected return, striking out nine without a walk -- he hit three batters -- over six shutout innings of three-hit work for Class A Stockton against visiting Visalia.
Gaudin, who had an All-Star-caliber first half (8-3, 2.88 ERA) in 2007 before lingering hip and foot injuries contributed to a disappointing post-All-Star break showing (3-10, 6.30 ERA), underwent surgery on Dec. 18 to repair a torn labrum in his left hip and to remove a bone his right foot.
He missed most of Spring Training while rehabbing and started the season on the 15-day disabled list, and he was scheduled to return to the rotation in mid-April. Injuries to Harden and Justin Duchscherer prompted the A's to activate Gaudin a week early, however, and he struggled in his first two starts of the season, going 0-1 with a 7.20 ERA.
In his four subsequent starts, Gaudin went 3-1 with a 2.42 ERA to help the A's rotation -- Opening Day starter Joe Blanton, Gaudin and Duchscherer, and newcomers Greg Smith and Dana Eveland -- to the lowest ERA in the American League through Tuesday, at 3.31.
"That's a tough decision," said starting catcher Kurt Suzuki. "Everybody's pitching so well."
"I'm assuming it will be me or Greg," Eveland said before the move was announced. "We're the young guys."
Gaudin, who went 4-2 with a 3.09 ERA in 55 relief appearances in 2006, suggested that a move to the bullpen -- and the dramatic change in routine it would bring -- might not be the best thing for his health.
"Coming back from the surgeries, it takes me more time to recover from pitching now," he explained. "You don't have much time to bounce back [working in the bullpen] because you have to be ready to go every day."
In theory, the A's bullpen, which entered Wednesday's game with the best ERA (2.63) in the Majors, will be so deep with the addition of Gaudin that the relievers won't often be asked to pitch on consecutive days.
"It does allow you to let a guy go out for that second inning and not worry about not having him for the next day," Geren said. "It gives you a bit of flexibility, and that definitely helps on decisions like that."
Talking about Oakland's pitching situation as a whole, general manager Billy Beane echoed Geren's assertion that having six quality Major League starters is a good problem to have.
"Our pitching needs to be organic; it's the one area we can't go out and sign," Beane said before Wednesday's game. "We've got spots for all our pitchers. If you have pitching, you have a chance at every game. This is the spot we hoped we'd be in, we just didn't anticipate it so early."
Harden was 1-0 with a 0.82 ERA in two starts before being placed on the 15-day disabled list with a muscle strain under his right shoulder blade. He's penciled in to start for Oakland on Sunday in the finale of a three-game series at Texas.
With righty reliever Keith Foulke (neck) expected to come off the 15-day DL for the Friday opener in Texas, the A's likely will send lefty Dallas Braden to Triple-A Sacramento to make room. They'll have to make another roster move when Harden is officially activated on Sunday, but Geren still isn't tipping his hand as to what that move will be.