A sweeping brass staircase in the Russell Senate Office Building? Whoopi Goldberg slides down it.

A ride on the underground trains from the Russell Building to the Capitol? Robin Williams yells "Let's race!" and then, his voice growing deep and inspirational as that of a born documentary narrator, he booms, "THE WIDE WORLD OF POLITICS IS NOW OPEN TO YOU!"

A press conference, complete with four senators and what seem to be several million cameras? Billy Crystal plays it straight, but everyone else is playing Billy Crystal. To a spurt of comic nonsense behind him, Sen. Edward Kennedy has the response of the day: "Mahhhvelous!"

The comics have come to Washington.

Goldberg, Williams and Crystal are spending Wednesday afternoon promoting the latest in call-in philanthropy, Comic Relief, which will raise money for the homeless on HBO later this month. And in the process, redefining the concept of the press conference and the whirlwind tour of Washington.

"President Marcos is homeless," Williams begins to the reporters and already giggling Hill staffers crammed into the conference. "We'd like to help him if we can. Send him to Club Fled."

From somewhere near the back of the tangle of technology, a photographer whose view is blocked shouts, "Down!"

The three comedians fall to their knees as if one.

Crystal, who in his pin-striped suit and regulation burgundy tie looks like a lobbyist with a good tailor, tells the crowd, "I was in a shelter in Seattle, and a man ran up to me. 'Billy, do me one favor -- show them we're not all bums.' "

Voice from the technology: "DOWN!"

"On my punch line you yell, 'Down!' " Crystal says. "This is a tough room."

The three have already been greeted by Kennedy in his office, where the senator showed them the dog tags that belonged to John Kennedy, framed letters from his children and mother, photographs of Ethiopia. They have been pursued by squealing Senate pages and interns. They have heard Comic Relief hailed by its creator, Bob Zmuda, as an "unprecedented event in the annals of American humor," and themselves called "three of the most caring people" in America.

This is not a day for restraint.

On the Road

Swaddled in dark limousine leather, the three sit silent for a moment.

"Inspired and terrified -- a very unusual feeling," says Williams.

"There's a picture of Sen. Mike Mansfield standing over you," says Crystal. "Ted Kennedy is in front, the voice is the voice you've heard and he's big, there. Unbelievable. I'm blown."

Then, with a grin, he is once again Billy Crystal.

"I looked good. I had a good suit. Fritz Hollings walked by."

"You do feel like a Capra movie," says a Williams so subdued one worries he may be ill.

But enough inspiration. Time to imitate Clint Eastwood, the aforementioned Kennedy, the earnest young men in Kennedy's office, the "Save the Shrimp" people, to shoot jokes at each other like caroming pool balls, to slide through a wardrobe of personality changes as extensive as Imelda Marcos' wardrobe.

"What's that on the left?" Goldberg asks as the car circles the Capitol.

The Supreme Court.

"Ooh, Diana Ross!" Williams yelps and bursts into song: " 'Ooh you can't hurry love . . . ' "

"That building on the right?"

The new Smithsonian museum complex.

"That's the Dolly Parton wing," Williams says as the huge, round domes slide by.

"Where are we going?"

The House of Ruth, a shelter for homeless women.

"I thought they said the House of Pancakes," says Crystal.

"The International House of Ruth," continues Williams.

"IHOR," finishes Crystal.

"It's beautiful," says Williams as the car glides by the Tidal Basin.

"It's like Paris," says Goldberg.

"Paris without the attitude," says Williams.

The limousine driver, unsuccessfully squelching a chuckle, drives on as the kids continue the game of "Can You Top This?"

The Monument

To "kill some time" before arriving at the International House of Ruth, the motorcade of cars, filled with press reps, managers, hangers-on and the all-important "talent" as the three are called, stop at the Vietnam Veterans Memorial.

"We're going to be mobbed," one of them says as the eyes of tourists light up.

They are mobbed.

A girl close to hysteria stands above the monument, her shrill voice harsh through the silence as Crystal and Goldberg look for the name of one of his high school friends.

"THAT'S ROBIN WILLIAMS AND BILLY CRYSTAL AND Y'ALL ARE JUST SO CALM!" she shrieks to her companions. "THAT'S WHOOPI GOLDBERG! GET OUT YOUR CAMERAS!"

Crystal finds the name, and while a park guard does a rubbing of it for him, Crystal stands with Goldberg's arm around him, his face contorted as if to hold back tears. The cameras jostle for position.

Williams has retreated to the car. When the others rejoin him, he is deep in the seat. "I didn't want to hang out with everyone jumping around," he says. "People came here to see their relatives. They shouldn't start that stuff here."

"We were really close," says Crystal. "We went to high school together, we grew up and went to college, he went to the Army -- it's the first time I've seen him since we graduated. We were really close. He was a crazy man."

The Shelter

This is Whoopi's place.

"Whoopi! Whoopi! Whoopi!" chant the women outside, the women inside, the women everywhere. She is handed tiny babies to hold, embraced, adored.

"As you can tell, this is not the kind of event we're used to," says House of Ruth Director Sandy Brawders to the media mob that has relocated from the Capitol. "Many of you have never been here before. We hope you'll return again sometime."

She then thanks the three.

"The reason we'd like to thank them is not just because of the money they'll bring, but because they have told us by coming here that we're worth the best."

"Whoopi!" a woman yells. "I need your autograph bad!"

Then, more mania, as Zmuda reads the list of participating comics and Williams pulls the crowd into a shouting response.

"Steve Allen!"

"You got it!"

"Sid Caesar!"

"Amen!"

"Michael J. Fox!"

"Uh huh!"

"Estelle Getty!"

"Amen again!"

Finally, it is Whoopi's turn.

"I'm looking around and it's family," she says. "I'm looking around and it's family and it's killing me. Cause we're in Washington, you know! It's heavy. Two years ago I was on welfare. Now, a welfare lady came to my show and she said, 'Oh, Miss Goldberg, it's so good to see people like yourself picking yourself up.' I said, 'If you'd gotten your foot off my neck I'd have gotten up a lot sooner.'

"These people don't know . . . " she starts.

"What you've been through," comes a cry.

"Or where you are," says Goldberg.

Then Crystal, who says, " 'You look mahvelous' doesn't fit here.' "

And Williams, who holds a baby up and says, "We have a spokesman here. She's only going to use vowels." He pulls his hat over the baby's face as the cameras swarm in. "No pictures, please! No pictures. He's just going to the grand jury."

The talent is sucked into the crowd.

"I was watching Live Aid and I began to think," says Zmuda in a quiet room where he and the others take refuge. "The music community seemed to have a monopoly on altruism. I organized the benefit after Andy Kaufman died, for the American Cancer Society, and that really brought people together. Comedians have always been described as loners and as a little psychotic. People have very stereotypical images -- you can't do comedy to raise money for something serious -- but comedy has always played a role in relieving the pains of life. You don't have to look far back -- Charlie Chaplin's tramp."

Crystal, looking a little dazed, approaches Zmuda.

"I'm upset."

"You want to talk?" says Zmuda, who looks suddenly worried. A star is upset. What has gone wrong?

"I went through too much," says Crystal.

"Oh," says a relieved Zmuda. "The emotions."

Across the room, Carol Fennelly, companion to homeless activist Mitch Snyder, is crying. Snyder is on a hunger strike to attempt to force President Reagan to remodel the Community for Creative Non-Violence shelter, and Fennelly wants Robin Williams and the others to visit Snyder there.

"They don't want to mix politics with this," she says, thin and drawn from her own fast.

Goldberg is talking to House of Ruth workers.

"I've been involved with people without homes for about eight years," she says in the deep, husky voice that, a little tired, a little smoke-worn, suggests it is perpetually the morning after. "It's not new. It's a problem that's getting larger and larger and larger and there seems to be no comfort from the government. You see 5-day-old babies in a shelter -- it makes you wonder what's happened to the American dream. Whenever I go on tour I go to a shelter in the city and see what I can do. Sometimes you feed people. You buy Pampers. You go shopping."

After Whoopi passes, Denise Speed shouts to a friend: "I got three Whoopi hugs!"

"I got three hugs from Whoopi and a kiss and an autograph," Speed says. Speed has been living in the shelter for two weeks due to what she calls "financial problems and whatnot." Along with about 60 other women from the Emergency Shelter at 10th and G streets NE, one of several House of Ruth facilities, she saw Goldberg's Oscar-nominated performance in the film "The Color Purple" the week before. "I thought she was very good at portraying an abused black woman. Just looking at that woman's face -- she went through some stuff, real deep. I know she went though hell."

Outside, mothers are holding their children high so they can see into the limousine as it pulls away from the curb. Then, with a quick turn and a whoosh of black metal, the cars are gone.