SCENE: Floor of the United States Senate. A young woman is standing near a first-term Republican senator, who appears to be pouting, chin down, hands thrust into his pockets.

Susan Alvarado recalls the conversation:

"What's going on at the White House tonight?" he asks her nonchalantly.

"The candlelight tour of the East Wing," she says. "Aren't you going?"

"I didn't receive an invitation," he says sullenly. "And I'm really mad at the White House."

"Senator, are you sure?" the earnest young woman replies. "It must have been some sort of mistake. Let me check."

She leaves the floor of the Senate, makes a few phone calls from her office and returns with the invite, saying his name had inadvertently been left off the list.

"It was an oversight," she explains.

But the senator is so stung by the slight that he later refuses to attend the ceremony. "The invitation was after the fact," Alvarado says now. "I guess the thrill was gone."

"These are the kinds of things I do all day," says Alvarado, who found her thrill on Capitol Hill as Vice President George Bush's $42,000-a-year legislative assistant. She's the first woman to hold the title. "I'm the pulse beat of the Senate," she says: trouble-shooter, favor-broker and douser of small fires for Bush, who also serves as president of the Senate.

"I think I have the best job in the administration," she boasts. "Am I the luckiest woman in Washington? I think I'm the luckiest person period."

Pre-dawn tennis with Laxalt, lunch with Kassebaum, huddle with Hayakawa, White House dinner with Schmitt, Saturday workouts with Weicker, p.m. tennis with Mattingly.

"I don't pretend to be exceptionally bright," she says. "I'm above average. But because of my background, I know people and I know how to get along with them. To me, it's inexcusable that a Republican senator wasn't invited to the candlelight tour. It could be seen as petty, but life is like that. Just because this is the Senate doesn't mean people aren't immature at times."

Taut and tomboyish with sleek dark hair cut in a Dorothy Hamill wedge, Alvarado is terminally preppy: crisp blouses with little bow ties, blazers, pleated skirts, no-nonsense stockings and sensible shoes that go click-click down the marble corridors of the Capitol. There's a jar of Jelly Bellys on her desk and a copy of "Power: How To Get It, How To Use It" on her bookshelf. She says "gosh" and "golly" and thinks the senators are "neat." Her name is listed in Washington's social register, The Green Book. "Cosmopolitan" magazine recently picked her as a woman to watch in the nation's capital.

She's 27 years old.

7:15 a.m. "Nice shot, senator," she calls, lunging for the speeding ball. Alvarado and Sen. Paul Laxalt (R-Nev.) are the only players on the indoor courts at Belle Haven Country Club in Alexandria.

"You hurt?" Laxalt calls.

"Only my pride," she laughs.

Laxalt serves again. An ace. "That is TOO good, senator," she says, switching sides. "Nice shot."

She is an intense player, fast and strong. Her strokes are powerful, her serve substantial. She wears a blue nylon warm-up suit, which is peeled off after the first set. She is perspiring, the rosy cheeks flushed with the fire of competition. Next month, she plans to try out for the Avon women's tennis championship. Martina, Tracy and Susan . . .

"I heard tape," she calls over the net, to verify that Laxalt's deep return was inbounds. "Nice shot."

Laxalt is still in his warm-up suit, not a drop of sweat on his silver-haired head. His strokes are masterful, placed with the precision of a finely tuned machine. He is pacing himself. She is sprinting. Tennis as a political metaphor: age and experience vs. youth and ambition.

Laxalt wins 6-3, 6-4.

8 a.m. She climbs into her bright red BMW and drives several miles back to the garden apartment condo she recently purchased. Since she gets up at 6 a.m., she has already read The Washington Post, The New York Times, The Wall Street Journal and The Los Angeles Times.

"I can't stand to sleep," she says, putting Vivaldi's "Four Seasons" on the stereo at full blast. "It sounds so corny, but I am so charged up every morning to get going, that tennis is something I really need. Otherwise I'm like a volcano, ready to erupt."

She comes across as a verbal jackhammer. "I'm hard to keep up with in a conversation for some people. I'm very hyperactive."

Born in Alexandria, the fifth of seven children, Alvarado grew up as an Air Force brat, moving from Madrid to Dayton to Anchorage. She went to a private Catholic girls' school before attending Ohio State University, where she played on the tennis team, was voted "Miss Congeniality" in the Miss OSU contest and earned a political science degree in three years. Her interest in Alaskan affairs landed her a job in the office of Sen. Ted Stevens (R-Alaska) as a staff aide. Two years later, when Stevens won the post of minority whip, Alvarado became the first woman leadership assistant to work on the Senate floor. She jumped from $11,000 a year to $18,000. She was 22. People thought she was a page.

"Psychologically it was very difficult. Emotionally it was very difficult because there were a lot of men, a lot of senators who were not too pleased to see a woman in their cloakroom listening to their jokes."

'Maxed Out' at $38,000

8:15 a.m. She changes into a pleated skirt and bright red blazer with a tiny Secret Service identification button on the lapel. On the wall of her condo is a framed copy of a 1978 newspaper article on her that Stevens inserted into the Congressional Record.

By 1980, Alvarado had "maxed out" at $38,000 a year working for Stevens. She wanted a new challenge. Stevens recommended her for the vice presidential assistant job.

"My friends said I was crazy, that you should work for the president. That the president's where it's happening, not the vice president. I was real nervous when I went for the interview. There were all these young people around and they're cuter than I am and they dressed better than I am and they're probably richer than I am and they're resenting me right away because I didn't work a day in the campaign but I was thinking I had the experience and the expertise. I could feel the poison looks I was getting, but anyway I went into the office and there was this admiral there and we talked and he didn't mention salary, so then I went in to see the vice president. He was kinda nervous. He was probably wondering, 'God, she's so YOUNG, she can't offer me anything, where did she come from?' "

(Pause for breath) "The thing is, senators are notorious for pawning off staff on other people. Bad staff. But they'll do it because they've got to get them another job and they figure, 'If I've gotten rid of 'em, they can get rid of 'em . . . The vice president said, 'How much do you want to make?' and this admiral said, 'Don't worry about that.' We went out in the hallway. All the Secret Service agents and me, and the admiral's standing there and he says, 'Well, you're making $38,000. We can match that.' I said I didn't want it matched, I wanted MORE than that. He said, 'Okay, $40,000.' I said, '$42,000 and you got a deal.' He said, 'Deal.' "

But Alvarado says she's earning approximately $10,000 less than a man would earn in the same position. "I think I'm worth every penny of it, to tell you the truth, at the maximum, but it doesn't bother me because I'm 27 years old and for $42,000 to be swallowed in Peoria is a heck of a lot of money."

9 a.m. The BMW zooms over Wilson Bridge. Alvarado's running late. She's usually at the Capitol by 7:30 a.m., drinking coffee in the Senate dining room. A government car then picks her up and chauffeurs her one mile down Pennsylvania Avenue to the White House, where she meets with President Reagan's congressional liaison and others. After that, she goes to Bush's office in the West Wing to pick up a copy of his schedule.

"I make rounds, talk to people, see what's cookin', then go over to the Executive Office Building, check in with everybody there. I like to be back on the Hill no later than 10 a.m. because this is where I'm supposed to be."

She pulls the BMW into a choice parking spot several feet from the Capitol steps. The guard greets her by name.

She strides to the elevators, chatting to several senators and aides in the bustling hallway. (Alvarado, says Becky Gernhardt, who works in Ted Stevens' office, is probably better known in the halls of the Capitol than some of the senators themselves.) Alvarado's office is on the second floor, several feet from the Senate chamber. She pushes against the heavy wooden door.

"OKAY EVERYBODY WAKE UP," she calls. Her two secretaries look startled. The office is large and tastefully furnished in beige and leather, with a fireplace against one wall. Painted on the huge, ornate ceiling is a colorful fresco, illuminated by a crystal chandelier the size of a small foreign car.

9:30 a.m. She flips through a few phone messages, while her secretary hands her a cup of coffee. Behind her chair is a telephone with 30 buttons. On the right hand side are the instant-dial-type buttons for numbers most frequently called: "The White House," "Cloakroom," "V.P.," "Mom," "Dad."

On the wall are framed autographed pictures: Alvarado with Bush, Alvarado with Sen. Robert Byrd (D-W.Va.), Alvarado with Sen. John Warner (R-Va.) and Elizabeth Taylor, Alvarado with tennis star Arthur Ashe.

She picks up the phone.

"Hi, is Billy there please? . . . Billy? Susan Alvarado, how are you? How's the senator doin' this morning. He is? Well, he ought to talk to Senator [Mack] Mattingly [R-Ga.]. I know he's looking for one, too. Yeah. Well, I can't play during the day, but perhaps later this evening . . . Okay. Great. Thanks, Billy. Bye-bye."

She hands a visitor a chrome ballpoint pen with the vice presidential seal and George Bush's signature.

"I give them to everybody," she says.

She takes the visitor's business card and instinctively runs her fingers over the surface. To see if it's embossed?

"Yeah. You know they're important if they're embossed. Someone told me that once so I went out and got these cards. They said, 'Now, Susan, it's not because you need to impress people. It's that they won't take you seriously unless you have embossed cards.' "

Alvarado tells her secretary to call for a government car. After one or two more calls, she pulls on her Chesterfield coat and heads for the door. She hands out one of her business cards. Embossed.

'Shortchanged as a Girl'

9:45 a.m. The black chauffeured car eases into the traffic on Pennsylvania Avenue. Alvarado sits in the back seat, chewing gum.

"I felt I was shortchanged as a girl, you know, in terms of opportunities and things, but I did everything I wanted to do. My one fear is that I come across too masculine. Only because I try to neuterize my own sex, to be taken seriously as a professional. You've got to be careful how women perceive you. They're the ones who are watching you with the daggers out."

Initially, Alvarado refused to date anyone on the Hill. Now, she's amended that policy. Yes, she says, she has dated a few senators.

"You're that much more marketable on the social scene. If you're dating a senator or a congressman, you're much more fun to bring around. 'Here's Susan. She works for George Bush.' They think that's the great part of it . . . If you can get a two-fer out of the relationship, not just one person being famous, of course it's fun that way for the host or hostess.

"You really have to be superhuman to pass up some of the temptations. There are a lot of really attractive congressmen, married or whatever. It really tests every kind of moral fiber in your body."

She says many of the senators see her as a surrogate daughter. "Drives 'em crazy. They're always trying to fix me up with their sons. If you look at a lot of political parents, you can see that their children aren't necessarily chips off the old block or they're not very successful in many ways in the public life as their mother or father. I think I am everything that someone's daughter isn't."

She takes another breath.

"There are a lot of young women who have set us back about 15 steps every day when they put the make on their boss. Young girls who are awed by the fact that they're with a senator. I used to laugh because some of these guys, appearance-wise, are a 5. All of a sudden, you attach a congressman or senator to his name and he immediately goes up to a 7 or an 8."

Alvarado says she's proud of the fact that she started inviting senators to her apartment for small, off-the-record dinner parties with "young people who would not normally be invited to parties where senators would be, and if they were, by chance, wouldn't be sitting next to them."

Senators "are lonely just like everybody else," Alvarado says. "Just to see them as individuals, to talk about 'Evita' or whatever they want to talk about. I caution the senator not to talk the whole time."

Another fun thing, she says, "is getting to know House people. Everyone on the Senate side kids about the House members in the triple knits and all that, but I just find that they're so much more down-home."

10 a.m. She strides down the corridor of the Executive Office Building, greeting Bush staffers, popping her head into offices, pressing the flesh like an experienced candidate. She's a cheerleader, an eternal optimist, Mary Poppins in Pappagallos and politics.

"My biggest accomplishment so far is that I've turned the corner in winning the vice president's confidence," she says. "And also the confidence of his staff, who were leery at first. And as a woman, I feel like I've succeeded against a lot of odds working in a man's world."

'I'm Just Running'

10:45 a.m. She enters the West Wing of the White House, shakes more hands, greets more people, sprints up the stairs to Bush's office past Secret Service men.

"That's the Oval Office, that's Deaver's office, that's Baker's office . . ."

She stops by the kitchen of the White House mess and greets the workers. Following her is like being on a campaign trail. What's she running for?

"Nothing. I'm just running," she laughs, grabbing a Tab and hustling out the door to the waiting government car.

"Isn't this neat?" she says, settling into the back seat. "Now we can go back to civilization. The best part about not working at The White House, I mean there everybody's fighting for territory. You can walk out and not look for stab wounds in your back. People stay away from congressional affairs pretty much. We make people stay out of it."

11 a.m. The Senate is in session. A male voice drones on from the intercom on the side table in the office while Alvarado waits for Bush to arrive. Sen. Nancy Kassebaum (R-Kan.) is on the phone.

"Senator . . . I'm sorry to keep you holding. Oh, great. 12:30? Uh, quarter to 1 or 1 would be better, but if you have to . . . Oh, you do? Okay, then, how about quarter to 1 then, yeah. Oh, you wanna go earlier. Then let's make it 12:30."

A page comes in. Sen. S.I. Hayakawa (R-Calif.) wants her. "He probably wants to read some poetry," Alvarado says, sprinting out the door to the Senate floor.

Alvarado moves skillfully along the Senate floor, whispering in ears. She returns to the office, cheeks flushed.

"She's good at it," says one Senate official. "She knows the floor. They know her. She knows the system and how it works. They couldn't have made a better choice. She's got the experience up here. She's respectful of the senators, and they like that."

Sen. Roger Jepsen (R-Iowa) arrives at the door, hugs Alvarado and hands her a brown paper bag. She spills the contents on the coffee table: Jolly Time popcorn, a tin of pumpkin pie spice, a small container of Mr. Pepper pepper and a hunk of blue cheese. Products from his home state.

The phone rings. Bush has arrived. She darts out the door to his plush, private office off the Senate chamber. Bush is on the phone. Alvarado hands him some papers. He peers over his eyeglasses. She speaks softly, handing him an envelope. He nods. He's due at a meeting.

What would the vice president do without Alvarado?

"We'd be lost," Bush says, exiting with a gaggle of Secret Service men.

Alvarado beams, and heads down to the Senate dining room for lunch with Nancy Kassebaum.

In the Flow

At 2 p.m., she's off to the Capital Hilton for an "Outstanding Young Women of America" reception. Later that afternoon, she will spend hours on the Senate floor, a figure in the shadows, the unidentified, anxious young face peering over the shoulders of the powerful in newspaper pictures and on the evening news. The Aide.

Her highest visibility so far came during the AWACS debate, says Tom Griscomb, press secretary to Sen. Howard Baker (R-Tenn.), during which she acted as a vital conduit of information between the president of the Senate and the legislators.

"Be in the flow," is how Alvarado describes it.

But many of her duties revolve around placating senators who want Bush for some reason or other. If a senator has asked Bush to appear at a fund-raiser and the answer is no, Alvarado will be called to intercede. Especially if the senator is running for reelection, she notes.

"I'm here to make their relationship with the vice president as smooth as possible," she says. "I think it's a big job."

A friend gave her the book on power. Inscribed on the flyleaf are the words, "Power may be the ultimate aphrodisiac, but knowledge is the ultimate key to power. Dedicated with best wishes for success to the first woman nominee for President of the USA in year 2000."

She hasn't really decided yet whether to run for political office. "The fun thing for me is just to be there, to watch it all happen, know these men and women as movers and shakers, as individuals, as personalities. I can see it all from the inside."

And what does Alvarado believe in? The Equal Rights Amendment. A strong defense budget. America.

"I think we're finally getting this country on the right track," she says. "This administration has been sensitive to the needs of the American public. I think people are happy to be Americans again! The economy, as bad as it is, has gotten people's attention. It's been a humble experience for the American people."

At 6 p.m., she leaves for a Community Health Service reception at the Four Seasons Hotel. Then she drives to her condo, changes and meets Sen. Mattingly at the Mount Vernon Racquet World indoor courts for a 9 p.m. tennis date. She gets home at 10:15, has dinner, reads until 1 a.m. and falls asleep for five hours.

Yes, she says, she is aware of the high mortality rate among the young and the restless on Capitol Hill. "It burns people out. I'm aware of it," she says. "But I don't intend to burn out. No way."