The West Terrace of the Capitol is about as unlikely a place as you can imagine for an adoption ceremony conducted by members of the Sioux Indian tribe, but hey, that's Hollywood.

Or at least Hollywood on the Potomac. Which is what Washington turned into yesterday after Kevin Costner and just about everybody involved in his new film, "Dances With Wolves," arrived for last night's world premiere of the film at the Uptown Theater, a benefit for the Smithsonian's new National Museum of the American Indian as well as its Resident Associates Program.

And Washington didn't let Costner and company -- or the Lakota Sioux who flew here to be part of the celebration -- down. A lunchtime reception at the Capitol hosted by Sen. Daniel Inouye (D-Hawaii), chairman of the Senate Select Committee on Indian Affairs, was everything a big-deal Hill event could be expected to be: Overcrowded. Ogled by tourists. Protected by lots of Capitol cops.

This time, however, the standard dress-for-success Washington crowd was enlivened by the aura of visiting luminaries -- Indians in buckskins and beads, Hollywood executives in very good haircuts, hangers-on in thigh-high skirts.

"There's something going on," mumbled one stunned tourist as he made his way past the souvenir stand just outside the reception room.

"They thought I was Kevin Costner, but I didn't have my hairpiece," joked a jovial Sen. Alan Simpson (R-Wyo.) after posing for camera-laden onlookers as he struggled out of the room.

After the reception, Native Americans were a significant portion of the crowd at the adoption ceremony, in which Costner (who starred in, directed and co-produced "Wolves"), actress Mary McDonnell and co-producer Jim Wilson were adopted into the families of some of the Lakota Sioux who had worked on the film.

"The idea is to honor Kevin and Mary and Jim on behalf of the Indian Lakota nation," explained Floyd Red Crow Westerman, who plays Chief Ten Bears in the movie. "They will all become part of one family."

With flags flying under the bright blue sky and the Capitol as a Central Casting backdrop, three Lakota Sioux guided Costner, McDonnell and Wilson through the ritual. After the Ironwood Singers, a drum group from South Dakota (where the film was made), beat out the rhythms of a song announcing the adoptions to west, north, east and south and to the earth and sky, the three were presented with shawls decorated with quilted star patterns and eagle feathers.

Albert Whitehat, a Lakota elder who was a cultural adviser for the film and who adopted Costner, spoke of his experience getting to know the actor. "When the movie was done, one of my granddaughters, who was an extra, kept on saying 'Kevin this' and 'Kevin that.' 'What is this first-name basis?' I asked. 'And what kind of a guy is this Kevin? We ought to check him out.' Now we all admire and respect his courage to break the barriers for us in bringing our two cultures together."

In Washington terms, the location of the event was not inappropriate. Close to the Mall site where the new National Museum of the American Indian will be built, the ceremony was clearly moving to the crowd as well as to the actors.

"The whole thing grew out of the giveback that Indians do," explained Christine LaMonte, senior vice president for publicity and promotion for Orion Pictures, which is releasing and distributing the film. "When someone gives you a gift, you give it back to them. Kevin felt the Lakotas gave him their cooperation and trust.

"And we knew that there was a new American Indian museum and thought how wonderful to be able to give them something more by giving them the film to raise money for the museum. So we approached the Smithsonian to ask them if they wanted to use the film as a benefit."

At $100 a ticket for both the film and a post-screening reception at the Sequoia Restaurant ($25 for the film, popcorn and soda), last night's premiere was expected to raise as much as $50,000.

"I think the real significance of this event is that the picture -- by the way it deals with Indian culture -- has many parallels with what we need to do at the National Museum of the American Indian," said W. Richard West Jr., the director of the new museum and a member of the Cheyenne-Arapaho tribes, yesterday afternoon.

"This movie speaks quite literally through the Indian tongue {almost a third of the dialogue is in Lakota}, and that is a powerful metaphor for what the Indian museum has to be. It has to be seen through Indian eyes and articulate its interpretation with Indian voices."

For Costner, it was even more basic. "I used to play at the notion of cowboys and Indians," he said after the adoption ceremony. "I don't know why, but I always wanted to be the Indian."

Yesterday his wish came true.