T.R. Knight, left, and Isaiah Washington pose together in August 2006. Washington will do an ad for a gay rights group to make up for a slur against Knight. ((Matt Sayles/Associated Press))

Grey's Anatomy actor Isaiah Washington, who got in trouble over an anti-gay slur earlier this year, plans to make it up to the homosexual community with an advocacy ad.

He has agreed to appear in a public service announcement on behalf of the Gay & Lesbian Alliance Against Defamation and the Gay, Lesbian & Straight Education Network.

"We're gonna have — I want to say at least two versions of it at this point. We may broaden our message a little," the actor's publicist, Howard Bragman, said Wednesday.

U.S. network ABC, which reprimanded Washington over the slur, was planning to shoot the ad in the next few weeks, Bragman said.

Washington was reported to have uttered the slur against Grey's Anatomy co-star T.R. Night last October.

The story came to light in January, when he used the term again in a backstage press conference at the Golden Globes while denying he had insulted a fellow cast member.

After being criticized by GLAAD, a gay and lesbian advocacy group, and the ABC network, Washington issued an apology and sought counselling.

No details of the public service announcement or when it is to be aired have been released.

With files from the Associated Press