It was Streep's third Academy Award, but her first since winning the Oscar for "Sophie's Choice" in 1982. She was also honored for the 1979 film "Kramer vs. Kramer," and had long been considered overdue for another Academy Award.

Accepting her award, Streep sounded less like a winning actress than a star who had just received a lifetime achievement award.

"I really understand that I'll never be up here again," she said in an emotional speech in which she congratulated Roy Helland, her hair stylist for 37 years and who shared this year's Oscar for makeup with Mark Coulier for "The Iron Lady."

"I look out there and I see my life before my eyes," said Streep, addressing an audience packed with the biggest names in the movie industry .

"When they called my name," said Streep. "I had the feeling I could hear half of America going, 'oh, no. Come on.'"

Streep, 62, is widely regarded as the best living movie actress, and most critics said she turned in her best performance ever as Thatcher.

She won her first Oscar at the age of 30 for "Kramer vs. Kramer," her fourth feature, according to the movie website IMDB.

"I was a kid when I received the first nomination," she said in comments to reporters backstage. "Two of the nominees (tonight) weren't even conceived."

In "The Iron Lady," she plays the feisty British leader both as a woman at the height of her powers in the 1980s, and as an old and lonely woman suffering from dementia in the present day.

Streep first appeared on screen in 1977 in "Julia" after having honed her craft at the Yale School of Drama and on stage.

She quickly became known for the depth and breadth of her characterizations, and for her gift with accents such as the Polish Holocaust survivor she played in "Sophie's Choice".

Dozens of other movies followed, ranging from romantic fare like "Out of Africa" and "The Bridges of Madison County" to biographical movies such as "Silkwood", and dramas like "Doubt" and the HBO television series "Angels in America" for which Streep won an Emmy.

She was presented the Oscar by Colin Firth, who won a statue for best actor last year for "The King's Speech" and who starred with Streep in the 2008 film "Mamma Mia!"

"Mamma Mia," joked Colin Firth. "We were in Greece, I was gay, I probably fathered her daughter."

In 2006, Streep changed direction to comedy, playing a ferocious fashion boss in "The Devil Wears Prada" and then camping it up in her first musical "Mamma Mia!".

She followed up with a dead-on impersonation of TV cook Julia Child in "Julie & Julia" and showed her flair for romantic comedy with "It's Complicated" opposite Alec Baldwin.

"You are unreasonably good," Firth said to Streep in his introduction before announcing the name of the winner." "Whatever role you play you raise the bar, making it a little more difficult for the rest of us."

(Reporting by Chris Michaud; Editing by Jill Serjeant and Sandra Maler)

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