Billy Wagner has more pain and swelling in his pitching elbow, and the New York Mets’ All-Star closer is out indefinitely.

Wagner had an MRI exam today that revealed additional inflammation in his left elbow — an alarming sign after he spent most of the past two weeks resting his ailing arm. Now, the NL East leaders don’t know when he might be able to return to the mound, if at all, this season.

“I’m very frustrated, but there’s not much for me to do,” Wagner said. “I want to play. I want to compete. There’s only so much time in a career and I want to get out there and help my teammates. We’re in a great situation right now. We’re leading our division and we’ve got a great chance to go to the playoffs and you want to be a part of that.”

Could the Mets, slowed all season by an unreliable bullpen, reach the postseason without Wagner?

Good question.

The team had hoped to activate Wagner from the disabled list yesterday in Pittsburgh. But he felt discomfort in his elbow after throwing a simulated game Saturday and was sent back to New York for further evaluation.

“It’s a dangerous area. It is in the elbow. It is in the tendon,” general manager Omar Minaya said. “We didn’t expect to have more swelling today. You expected to have less swelling. And the fact that you have more swelling, that’s a concern. And that’s why if it goes that route we have to be more careful and be more conservative.”

Wagner’s absence has created a huge hole at the back of an already shaky bullpen as the Mets try to hold off Philadelphia and Florida in a tight division race. New York manager Jerry Manuel has been using a closer-by-committee approach, with mixed results at best.

“Who’s my closer? Who’s my closer?” a smiling Manuel said before tonight’s game against Atlanta, repeating the familiar question he’s been peppered with day after day. “We’ll just try to match up the best way we can.

“The thing I want to be careful of, at this stage of the season, is anointing someone as that person and then that doesn’t work out,” he added. “I do not necessarily determine the role. The relief pitcher determines the role.

“I’m considering everybody from the Gulf Coast League to Triple-A. Can any of y’all throw?”

Seeking more depth, the Mets acquired right-hander Luis Ayala from Washington on Sunday for a player to be named. Minaya said several major league closers have cleared waivers, making them eligible for a late-season trade. But he acknowledged there aren’t many attractive options out there.

“The reality is, true, proven guys are not going to get through,” he said.

Players must be on a team’s roster by August 31 to be eligible for the postseason with that club.

Minaya and Manuel said the Mets have considered moving a starting pitcher to the closer’s role — such as John Maine or Oliver Perez — but it sounded as though the team was leaning against it.

That means there’s added pressure on relievers such as Aaron Heilman, Pedro Feliciano and Scott Schoeneweis to perform well in roles they’re unaccustomed to.

“I feel comfortable that the answer, when Billy’s not here, is in that room,” Minaya said. “The guys in there are going to have to step up. I think we’ve got the guys.

“We’re not the only team that goes through this, and we have to find a way to get it done.”

Wagner said he expects to pitch again this season and he hasn’t been told he won’t. So far, doctors haven’t found any structural damage in his elbow, Minaya said, but the pitcher probably will be re-examined when the swelling subsides.

In the meantime, Wagner can play catch lightly and do other rehabilitation exercises. He is taking anti-inflammatories, but he won’t have a cortisone shot in his elbow. Doctors advised him that if he were to do that, a shot could mask a more serious injury and increase the chances of him blowing out his elbow.

Wagner said the additional inflammation is a result of him trying to come back too quickly. He threw hard in a rehab game with Double-A Binghamton last week.

The 37-year-old lefty is 0-1 with a 2.30 ERA and 27 saves in 34 chances. He is in the third season of a four-year, $43 million contract and ranks sixth on the career saves list with 385.

In other injury news, right fielder Ryan Church (post-concussion syndrome) was scheduled to play the outfield at Triple-A New Orleans for the second consecutive night.

Second baseman Luis Castillo (strained left hip flexor) also is on a minor league rehab assignment. He was slated to play Tuesday night for Binghamton.