BALTIMORE -- The Yankees are attempting something rare with Joba Chamberlain, hoping to complete his transition into their starting rotation without demoting him from the big league level.

The latest stage of that progression is set to take place on Wednesday, when the right-handed reliever could come in behind starter Andy Pettitte at Baltimore and throw 55 pitches -- or, if the game doesn't call for it, he may not pitch at all. By now, Chamberlain has learned to expect the unexpected.

"My short time here hasn't been anything normal," Chamberlain said. "I've got great support, so I think that makes it a little bit easier on the transition. It's exciting to know that you're being thought of in both aspects.

"This is what they see fit and we've got a lot of great guys in the bullpen, and a lot of great guys starting, too. I can learn from everybody and try to take it to make myself a better pitcher."

Chamberlain last appeared on Saturday against the Mariners, throwing two scoreless innings, setting a Major League career high with 40 pitches. It's a mark that will be short-lived, but the exact timetable for how long it will stand depends on the progress of the game and Pettitte's performance against the Orioles.

The benefit of keeping Chamberlain in the big leagues is obvious, in that every out he records helps the Yankees immediately. Now, it will also balance a question mark, because the team may not need those outs at the moment Chamberlain is ready to perform.

"We have it mapped out, but we also know that in that map, you'd better be ready to take some detours," Yankees manager Joe Girardi said.

To that end, the Yankees have considered the thought that they may use Pettitte for seven innings and then hand off to Chamberlain for one, just as they'd done when he was exclusively setting up for closer Mariano Rivera. Then again, if -- as Chamberlain wondered -- Pettitte pitches "a four-hit shutout," the next appearance could be pushed back to Friday at Minnesota.

"There's ways that we can be flexible [Wednesday] if we have to," Girardi said.

In the larger picture, Chamberlain's expanding workload also requires that he refine the command of his secondary pitches, after having enjoyed great success in the Major Leagues thus far primarily on the strength of his fastball and slider.

Chamberlain believes his curveball is just about ready for prime time, and the touch on his changeup is the one that comes and goes more often at this juncture -- good on some days, not so good on others. He said he uses the changeup every time he tosses a ball, be it across the outfield or warming up to come into a game.

"They're coming," Chamberlain said. "You've just got to continue to play catch with them and get a feel for them. That's the way it's going to come along."

Girardi said that he did not want Chamberlain to tinker with the curveball and changeup in game situations just for the sake of doing so -- as a pitcher might in Spring Training -- but Chamberlain is expressly cleared to use all four pitches whenever the individual batter or spot dictate it.

"You want to see him develop his other pitches when he has the opportunity to do it, but the first thing that I'm concerned about is building up the stamina," Girardi said.

Chamberlain has even started to watch the game like a starting pitcher, abandoning his usual post in the bullpen in favor of the dugout during the Yankees' recent games. Life in the rotation is closer than it may seem -- after Thursday's off-day, the Yankees are scheduled to play 17 consecutive days, which could bring a six-man rotation into play.

While Girardi and general manager Brian Cashman have not spoken about that possibility, Girardi said that, "At this point, I won't rule anything out." The potential to add Chamberlain to the Yankees' existing starting five remains -- at least for the moment.

"If you're going to do it, that's the time that it's a possibility," Girardi said.