Leonardo DiCaprio Works D.C.'s Green Carpet

Kuwaiti Ambassador Salem al-Sabah, right, and his wife, Rima, with Leonardo DiCaprio -- the surprise guest of honor at the al-Sabahs' Earth Day dinner. (Vicky Pombo)

If you're going to throw an Earth Day dinner, there's no better get than Leonardo DiCaprio.

The movie star/environmentalist -- just voted the greenest celeb -- was the big surprise at Wednesday night's Kuwait-America Foundation benefit hosted by Ambassador Salem al-Sabah and his wife, Rima. (DiCaprio, who was a last-minute no-show at last fall's National Italian American Foundation gala due to illness, flew in just for this event.) The 34-year-old actor charmed everyone in room by bringing his mom, Irmelin, as his date; making small talk with most of the guests (not reporters, but who can blame him?); and making the Washington crowd feel important.

"The more I get involved and learn about these issues, the more I realize that as important as the grass-roots environmental movement is, there will be no significant progress on the issue of climate change without action from our government," he said after accepting the night's Environmental award. "We need the government to offer incentives that automatically integrate the ecology into our marketplace and everyday living standards."

The hostess assembled her usual roster of A-listers: Secretary of State Hillary Clinton, NBC's Tom Brokaw, White House social secretary Desiree Rogers (in a black mini-dress), Sen. John Kerry, National Security Adviser Jim Jones, Mayor Adrian Fenty, former Treasury Secretary Hank Paulson, Justice Stephen Breyer and plenty of oil company execs who raised $1.5 million for Conservation International.

In honor of Earth Day, the chilled soup came in ice bowls set on plates of real grass. In honor of DiCaprio and Clinton, Marvin Hamlisch performed Dean Martin tunes (Leo's favorite -- go figure) and turned the lyrics of "Maria" from "West Side Story" into "Hillary." Does everything need to be recycled?