"You are the real thing, and I love you for it," said De Niro, who co-starred with Streep in "The Deer Hunter, and received the AFI Life Award last year.
Keaton, who starred with Streep in "Marvin's Room," called her "my generation's genius."
As she accepted the award Thursday night from director Mike Nichols, Streep joked about what it's like to hear so much praise from leading figures in the movie business.
"Can't we just do this every year?" she said. "I'm so proud and grateful, and I hope it's not the end."
Previous AFI Life Award recipients include Eastwood, Nicholson, Bette Davis, Kirk Douglas, Tom Hanks, Alfred Hitchcock, Jack Lemmon, Gregory Peck, Sidney Poitier, Steven Spielberg, James Stewart, Barbra Streisand and Elizabeth Taylor.
The presentation was taped for broadcast later this month over the USA Network.
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