WASHINGTON (Reuters) - Ellen DeGeneres, an American entertainer and prominent gay rights advocate, received the highest U.S. award for achievement in comedy on Monday.

Receiving the Mark Twain Prize for American Humor at the Kennedy Center, the national showcase for arts, DeGeneres was praised as a pioneering female comic whose edgy variety show has helped define the format for daytime television in recent years.

But several guests also highlighted the comedian's groundbreaking decision 15 years ago to go public with her sexual identity in a career-rattling move the comedian said was a necessary step for personal dignity.

"I did it for me and it happened to help a lot of other people and cause a big ruckus," DeGeneres, 54, told reporters before the tribute, summarizing her decision in 1997 to come out publicly as gay in tandem with her on-screen character in a move that sparked controversy and prompted some advertisers to flee.

The Twain prize, named after the 19th century satirist, is the nation's highest honor for achievements in comedy.

A native of New Orleans, DeGeneres spent her twenties as an itinerant comedian on the Los Angeles nightclub circuit until prominent spots on late night television led to her own prime time sitcom.

The original show, Ellen, featured DeGeneres in the lead role as a bookshop owner in an idiosyncratic neighborhood. While the show got a boost after the star came out of the closet, it was over a few years later.

She later returned to the standup stage, and hosted the 2001 Emmy awards, which was postponed twice after the September 11 attacks - a somewhat subdued celebration that allowed her to try to lighten the national mood.

Several guests said that DeGeneres brought a compassion to her comedy that is rare in the field.

"The rest of us comics come from really messed-up, dark childhoods. She might have come from that, I don't know. But it's not what she puts forth," said John Leguizamo, who joined the tributes. "She just puts out this beautiful goodwill."

In the last 10 seasons on television, DeGeneres has left her mark with a daytime variety show which she often uses as a way to promote a commitment to gay equality.

"For a lot of people, Ellen is their only homosexual friend," said late night talk show host Jimmy Kimmel.

DeGeneres is the forth woman to receive the award since its inception in 1998.

Comedian and actor Will Ferrell won last year. Past award winners have included Bob Newhart, Steve Martin, Richard Pryor and Bill Cosby.

Monday night's ceremony will be broadcast on PBS on October 30.