Jorge Posada will have season-ending surgery on his right shoulder, ending his attempt to return to the Yankees’ lineup for the team’s playoff push.

The five-time All-Star catcher has struggled with shoulder pain most of the season, weakening his throws and limiting his playing time behind the plate.

On the disabled list for the second time this year, Posada was trying to rehabilitate his shoulder enough to come back as a DH or first baseman this season. But after the Yankees acquired slugger Xavier Nady in a trade with Pittsburgh on Saturday, they determined it was best for Posada to have surgery now, the general manager, Brian Cashman, said yesterday.

“It’s just the obvious way to go,” Cashman explained.

Posada is expected to be sidelined at least six months and it’s not certain that he’ll be ready for the start of spring training in February, Cashman said.

“As difficult as it is, I can focus on coming back 100 percent for next season instead of coming back at less than that now,” Posada said in a statement. “Until then, I still plan on being a teammate and friend to the guys I share this room with. I may not be playing, but I want to be a part of this team and the run that we’re on.”

The Yankees won their first eight games after the All-Star break before losing Sunday night at Boston. They entered yesterday three games behind first-place Tampa Bay in the AL East and two back of the Red Sox.

New York announced the decision after Posada met with Cashman and manager Joe Girardi following batting practice. Cashman also spoke to co-chairmen Hank and Hal Steinbrenner to “make sure that they were all on board.”

“After speaking with Brian and Joe, we thought it was best for me — and the team — to have the surgery now,” Posada said. “I’ve always taken pride in being there for my team and playing every day with them. With Xavier here now, there isn’t as much pressure on me to return.”

Posada took some light swings from the left side during batting practice yesterday before New York played the Baltimore Orioles. Earlier in the afternoon, he said he still hoped he was in the team’s plans for this season.

No date has been set for the operation, Cashman said. It will be performed by New York Mets medical director Dr. David Altchek, a shoulder specialist who examined Posada last week.

An MRI showed fraying in the tendons around the labrum, but not a rotator cuff tear, Posada said then.

“The reason we were going through the process that we did before was basically we didn’t have someone to slot right in there as a hitter. Now we do with Xavier Nady. So it gives us the opportunity to move forward with Jorgie,” Cashman said. “He was willing to do what we wanted when there was a need, so he was delaying the surgery through that need. But now that we have a hitter, I think this was predictable.”