"Slumdog Millionaire," the story of a Mumbai slum dweller who hits the big time on a TV game show, won the prize for best ensemble cast in a motion picture. Sunday's SAG award followed four Golden Globes earlier this month and the Producer's Guild Award on Saturday night.

But the night did not belong wholly to the rags to riches independent movie, which came away with just one prize.

Sean Penn won the best actor award for playing slain San Francisco gay rights activist Harvey Milk in "Milk," while veteran Meryl Streep was a popular best actress winner for her role as a vindictive nun in the Catholic Church abuse drama "Doubt."

Neither "Milk" nor "Doubt" has featured strongly in the awards season so far but the Screen Actors Guild, in which Hollywood actors honour their peers, is known for throwing curveballs on the road to the Oscars.

"Milk" has played well in Los Angeles, where the gay community was embittered by a November 2008 referendum that banned same sex marriage in California. "This is a story about equal rights for all human beings," Penn said in his acceptance speech.

Streep paid tribute to other strong performances by women in the past year, adding, "There is no such thing as the best actress. There is no such thing as the greatest living actress," referring to the accolade often bestowed on her.

Australia's Heath Ledger, who died a year ago, added a SAG best supporting actor award to his tally for playing the Joker in Batman blockbuster "The Dark Knight."

POSTHUMOUS HONOR FOR LEDGER

Sunday's award, greeted by a standing ovation, makes Ledger a virtual shoo-in in February to join Peter Finch as the only two actors to win Oscars after their death. Finch won in 1976 for "Network."

British actress Kate Winslet won the best supporting actress SAG award for her role as a German woman with a hidden Nazi past in "The Reader."

Winslet, who is also Oscar nominated for the role, said it was the most challenging part she has ever played. "Playing Hanna Schmitz was such a blessing, even though it made me completely insane," Winslet said.

"The Curious Case of Benjamin Button," which has a leading 13 Oscar nominations, came away empty-handed on Sunday, as did "Frost/Nixon," which recounts journalist David Frost's interviews with disgraced U.S. president Richard Nixon.

David Poland, editor of Movie City News, said: "People admire 'Benjamin Button' but they don't love it. It is big and the acting is beautiful but it doesn't hit them emotionally."

Among television programs, which compete in separate categories, Tina Fey, Alec Baldwin and the cast of "30 Rock" swept the comedy awards, while "Mad Men," set among advertising industry players in the early 1960s, won best drama ensemble cast.