IT'S FRIDAY NIGHT BACKSTAGE at Harrah's Trump Plaza in Atlantic City and headliner Lynda Carter, in a white terry-cloth bathrobe, her "Wonder Woman" cleavage hidden beneath it, is talking to Marty Klein, one of her agents.

Klein is about to go catch the show of another client, Joel Grey, who has recently become a blond. The topic of hair color leads them to a discussion of the hair roots of Loni Anderson, Carter's erstwhile co-star in a short- lived TV series. Shirley Mac Carter asks Klein if he knows Clark Clifford. Wait a minute: Clark Clifford, White House counsel to Harry Truman? Secretary of Defense in the Johnson administration? Lawyer for Bert Lance? Yes, that Clark Clifford. Or, does Klein know Paul Warnke? That's Paul Warnke, former director of the Arms Control and Disarmament Agency, chief negotiator at the Strategic Arms Limitation Talks, and a member of the Trilateral Commission?

Klein doesn't know them. But Lynda Carter, who also knows Burt Reynolds and Richard Dreyfuss, does. Clifford and Warnke are the law partners of her second husband, Washington lawyer Robert Altman.

"It's a small but powerful law firm," Carter explains to Klein. She says of her husband of 18 months, who is seated in the living-room section of her dressing room, "When you hear lawyer, you think, how dull. But Robert is a very successful lawyer who loves rock and roll."

Carter, 34, became famous 10 years ago for twirling in place and being transformed from TV character Diana Prince, bespectacled Pentagon factotum, into the barely attired Wonder Woman. In her real life an ability to change personas has come in handy. She now switches back and forth from being the wife of a Washington lawyer to being a Bob-Mackie-gowned casino entertainer.

Carter and Altman are a sort of Baby Boom Liz Taylor and John Warner: she the flashy Hollywood beauty, he the low-key Washington insider. They have two homes, his comfortable brick house in Northwest Washington and her large California ranch. With Washington and Hollywood becoming ever more intertwined, they offer instructive insights into the connection.

As far as Hollywood is concerned, Altman is an amused cynic: "You do encounter people who if you asked them who is president, you're not sure they'd know, except that he's a former actor who did well."

As far as Washington is concerned, Carter gushes like a schoolgirl on a field trip: "Washington is the most exciting city I've ever been in. There's an energy, an excitement. It's the capital of the western world . . .

My close friends in Los Angeles are envious when I tell them stories I've heard," she says, mentioning, as an example, Clark Clifford's anecdotes about the Truman days.

"I've really been welcomed by some very special people. Not only to Robert, but in world history."

AS LYNDA CARTER she will be performing in Atlantic City and Las Vegas, appearing in photo spreads for Maybelline cosmetics, and filming two movies for CBS television.

But in her Northwest home, where she introduces herself as Lynda Carter Altman, she makes frequent references to her domesticity: "Here, I'm my husband's wife." And she says she and Altman are "very, very seriously" thinking about starting a family.

She is dressed in gray slacks, a matching cowl-necked sweater, a black jacket and a pair of low-heeled loafers with chains across them. On her left hand is a large diamond engagement ring; another finger displays rubies. On her wrist is a gold and diamond bracelet.

Hers are the looks of the prettiest girl in high school gone Hollywood. She is tall, 5 feet, 9 inches, with generous bust and hips and small waist. Her features are prom queen pert, punctuated by masses of dark hair ad huge, darkly outlined, turquoise eyes. It's easy to see how she won the part of Wonder Woman.

She occasionally veers into Valley Girl-ese, with exaggerated facial and vocal mannerisms. She says of the number of invitations and requests that come in: "My schedule is so hectic I'm unable to do many things. When you have to refuse a State Dinner . . . I was devastated. TWICE! It's so exciting, so special to be at the White House."

She seems to be working hard at getting right the role of Washington Wife. When asked to name the friends she has made here she hesitates. "I don't want to name drop. The Cliffords. They're really Robert's friends, they've been so gracious. The Symingtons," she pauses. "I don't think it's right. It's too show-bizzy."

The white brick home is full of large upholstered furniture, wing chairs, polished wood and bowls of flowers. A soft-rock radio station plays over hidden speakers. There are only a few reminders of celebrityhood: an autographed photo of Phyllis George, one of Clark Clifford, a wedding picture and a small photo in a heart-shaped frame of Carter as Wonder Woman.

"This is his, he had this," she says with a sweeping gesture. ifornia-style house in Potomac.

"On the West Coast I have an 18-acre ranch on the edge of a national forest. I have my truck, which I use to haul hay. My horse has a virus now, poor guy. That space and privacy I do want. I also need my own bathroom. I have my clothes in every closet -- poor Robert."

Washington is her real home now, she says emphatically. Her activities here are "a regular person's day. I do vocal exercises. Go to lunch with my husband as often as I can. I go to that gourmet place, Sutton Place Gourmet, and choose something fresh to make for dinner. I usually do the cooking. I make business phone calls. I read. It's restful."

But her forays into the quotidian frequently end in tumult. When she shows up in the supermarket, "People can't believe it. They say, 'What are you doing here? . . . Three or four times a day someone comes to the door. Or I'm followed . . .

IT IS LUNCHTIME at the Hay-Adams. At one table is Robert McNamara, at another is Nancy Reynolds, one of the first lady's closest friends. The walls are done in soothing yellow, potted flowers sit on the tables, tuxedoed waiters move by silently. Robert Altman, good-looking in an unobtrusive way, tall and dark, looks at home here in his discreet glen plaid suit, french cuff shirt and white pocket handkerchief he folds into three points.

At week's end he will be sitting in a booth in Harrah's Trump Plaza in Atlantic City, the place where all the leisure suits went to die, and with his french cuffs, and pocket handkerchief, he will look like a rising young lawyer who took the wrong exit off the New Jersey turnpike.

He sounds as if he is happy to be out of place when in Hollywood.

"When you go to large fund-raising affairs and parties (in Hollywood) there are some personalities that are hard to be with for extended periods. Some are absolutely neurotic. Some have amazing narcissistic complexes. It's not surprising given that business . . . You can be hot one day and cold the next.

"This is not to say you can't have fun at a party. You can think to yourself, 'This person is really nuts.' But it can be fun to deal with on a limited basis."

is conspicuous in Washington, to say the least, has had no effect on his career, he says.

"People are too sophisticated for that," he says. He adds that at most "when we're concluding a deal and we're going to have a dinner or something, some guy might say, be sure to bring your wife."

The effect on his social life, however, has been significant. Even Washingtonians who pride themselves on their jaded approach to the famous are clamoring to meet Wonder Woman. Altman says, "Invitations come to me and I say, why am I being invited? I don't know this person. Am I suddenly a more fascinating conversationalist? The reason is obvious. It doesn't bother me. People would like to have her at their dinner parties; it shows good taste. It can be two-edged. You can go to an interesting dinner party as a result."

CARTER WAS BORN in Arizona, the youngest of three children. Her parents divorced when she was young and her mother went to work as a lab technician for Motorola to support the family. Carter has had little contact with her father since. At age 15 Lynda began singing in the local pizza parlor to earn extra money. After high school she took off with a band and sang in Holiday Inns around the country, in the Catskills and Las Vegas lounges. Next, she won a succession of beauty contests, culminating in Miss USA. Shortly after that she was picked by producers to be the heroine of a TV show based on the "Wonder Woman" comics. The show, which made Carter famous, debuted in 1975. In 1977 she married her agent, Ron Samuels.

Their marriage ended in 1982.

Propelled by the success of "Wonder Woman" (canceled in 1979), she did a series of specials and made-for- TV movies and talked about going (but never went) to New York to study acting with the fabled Sanford Meisner, teacher of Gregory Peck, Joanne Woodward and Diane Keaton. She worked on her singing -- increasing her range by an octave -- for her return to Las Vegas, this time as a headliner. She also found time to be born again, a religious experience she downplays since her marriage to Altman by a rabbi.

Becoming Lynda Carter Altman is, she says, the most profound change in her life.

"Now I have a different goal: Robert and having a family and my career in addition . . . I want to start a family. It's time. I have the man I want. I have where I want to live. My brother and sister both have children. They started young. I've waited and now it's right."

She doesn't like to discuss her first marriage, but does make occasional references to it. "This is (Robert's) first marriage, my second. But for me, it's my first . . . Robert is my best friend. I've heard that phrase, your spouse is supposed to be your best friend. But I never experienced it before. He's for me and I'm for him. A friend doesn't try to control you, manipulate you." YOU COULD say Carter and Altman were brought together by Moisture Whip makeup.

Carter is a spokeswoman for Maybelline, the cosmetic firm owned by the pharmaceutical company Schering-Plough, a client of Altman's law firm. One evening they both found themselves at company headquarters in Memphis.

Altman recalls the evening, arranged by matchmaker R. Lee Jenkins, who runs Maybelline. "I was in Memphis for the day. Lee said Lynda Carter was in town, she helps with product development. When she comes it's an event, and they have a dinner for her.

"I knew she was a good-looking actress who modeled for Maybelline, but I couldn't quite place her. He said, 'Do you want to go to the dinner?' What are you going to say, 'No, I'm busy' -- I'm in Memphis. I was intending to go back to the hotel and watch a football game. I thought the last thing I need is to go to dinner and get mixed up with some Hollywood actress.

"I went. I sat next to her, and we hit it off immediately. There was a strong and immediate attraction, even to the point that we were so very interested in one another that it seemed rude to the rest of the table.

"After that I was definitely interested in seeing her. She was beautiful and fascinating, not at all what I had anticipated . . . I expected someone who was narcissistic, self-important and full of herself. But she is unpretentious, warm, funny and bright. I wanted to see her again.

"I had no notion at the time that it was going to end up in marriage. I probably would have said, it will be fun, that's it."

Carter looks like a love-struck ingenue when asked how she and Altman met. "Fate," she replies dreamily. Three days after their meeting in Memphis, Altman called Carter, who was then back in California. When she heard his voice she realized she was "head over heels."

They started a commuter romance. About a year after they met Altman flew to Monte Carlo for the weekend to visit Carter who was performing there. While on the French Riviera (haven't we seen this in the movies?) Altman proposed. They were married in California 18 months after they met.

IT IS EARLY afternoon in the casino at Harrah's Trump Plaza in Atlantic City, but it could be 3 a.m. There are no clocks and no windows. The players are mostly older people -- women at slot machines with plastic cups of quarters, men gathered around the craps table -- oblivious to everything but the game in front of them. The entertainment booked into the hotel seems designed as an antidote to the intensity: It offers nothing the patrons haven't seen on thousands of hours of television.

It's noon in the darkened theater and Johnny Harris, Carter's music director for the past eight years, is running the band through its final rehearsal. Harris, a charming Englishman, has also worked with Sammy Davis Jr., Petula Clark, the Muppets and Tom Jones. (He explains what happens to the room keys women wrap in their undies and throw at Jones: "He gives them to the road manager who puts them in a little box they drop in the river.")

Besides Harris, there is his wife, artistic director, Joyce Temple Harris; production manager and best friend Trish Malin; a sound man; a lighting designer; Carter's five-member band; and about 20 musicians employed by Harrah's.

At 1:50 Lynda arrives. Her high spike heels put her just above the six- foot mark, and she towers over practically everyone. Even though it is barely light enough to see she is wearing dark glasses, which she takes off only for a few minutes during the two-hour rehearsal.

There is a sense of deja vu watching her run through her renditions of "Footloose," "Neutron Dance" "On My Own," which are interrupted frequently to adjust lighting and sound levels. Finally the realization hits: it is just like the Carter Maybelline commercial in which she breaks away from rehearsal to tout the company's mascara.

At 4 Joyce Harris comes on stage to give Carter some advice. "Exaggerate the strut. Think SHOW BIZ," she says. As Harris demonstrates, Altman walks quietly on stage in back of Carter and puts his hands over her eyes.

She turns, yells "Honey!" and wraps her arms around him ecstatically. Then Carter, Altman and Joyce Harris sit down at one of the booths and go over some papers that Altman pulls from his briefcase.

CARTER AND Altman may try to pass themselves off as just another two-career couple, but not many Washington working women have received the Gold Poster Award, recognition that more than a million people have a picture of your smiling face tacked to the wall. Carter discusses her sex appeal as if it is something external; part of a uniform her job requires she wear.

"The way that I look and the way that I am are different," she says. "I've never been va-va-voom. I've never felt that way on stage, that I'm promoting sexuality. The dresses are cut that way, but my personality is not that way."

It's a contradiction, she says, "But a nice one. I don't want to alienate half the audience, which is female. You don't have to play on it if it's there visually . . . I'm not trying to turn anyone on. I'm just singing and dancing."

At the casinos, having a body that incites catcalls is expected as part of the cover charge. But in Washington Carter's looks draw a different sort of attention. Altman is asked whether he feels women they see socially are jealous of his wife.

"Simply stated, yes," he replies. "You can tell from the sideways glances, looking her up and down; the little remarks that are made. It's obvious there is a sense of envy . . . "

Altman also acknowledges that when he brought Wonder Woman home to meet mom and dad, who are both Washington lawyers, there was some apprehension.

"When a son or daughter marries, there is always a question whether or not it will work. And there were concerns given the very evident differences in our lifestyles. She has her own career, which is necessarily tied to the West Coast. There were concerns, but nothing that would be unusual."

A SIGN OUTSIDE Harrah's Trump Plaza Theatre advises that appropriate attire is required. At Harrah's, appropriate is broadly defined. The room, which holds 750 in its red banquettes, is about two- thirds full for Carter's first show at 8.

The opening act is a ventriloquist. After 25 minutes of him, the lights dim, the band strikes up "Lucy in the Sky With Diamonds," smoke billows across the stage and out comes Carter, in a black and white sequined Bob Mackie creation, slit to the top of her thigh, which through some feat of engineering never flaps open indiscreetly.

Watching the show with Altman is his father, Norman, who first came to Washington after graduation from Harvard Law School to work for the government during the New Deal.

"Are we gonna have fun tonight?" Lynda asks the audience, which responds in the affirmative.

"I didn't hear you," Lynda calls back.

The audience, including the two Altmans yells out "Yeah!"

She sings her first two numbers, "I've Got the Music in Me," and Lionel Richie's "Hello."

Robert, his eyes riveted on his wife, loosens his tie. His father pats him on the back and says, "She's great."

She next does a medley of "I'm All Right" and "Great Balls of Fire," and struts provocatively around the stage. After the audience applauds she says, "You sure know how to make a girl feel good."

"You're beautiful," calls out one man.

"Thank you, so are you," she calls back. Everyone claps some more.

While the band plays solo, Lynda disappears backstage. She reemerges amid more smoke to "Neutron Dance." She is wearing another Bob Mackie dress, sequined in turquoise and silver with the same leg slit as the first. This gown, however, bares a great deal more of Carter's torso. And in case the audience misses the point, asymmetrically placed sequined stars adorn either side of her cleavage.

"This is just a little rag I threw on," Carter says as the audience ooohhhhs its appreciation.

After she sings "Neutron Dance" she asks if anyone in the audience has a napkin she can wipe herself with. Suddenly the room looks as if it's declared a surrender; white napkins waving everywhere. She bends over at the waist and takes a napkin proffered from a man a ringside. She blots her forehead and neck then turns her back and blots her chest. Next, e napkin back, although no room keys wrapped in jockey shorts are tossed on-stage.

Carter does two shows a night, almost the same, but the midnight show is a little looser. To introduce her medley of Irving Berlin tunes, Carter says, "What I'd like to do now is take you down memory lane." But at the second show she gets as far as, "What I'd like to do now is take you down . . . " when a man in the audience yells, "Oh, my God!"

Lynda pauses, looks flustered then calls out, "I didn't mean it that way!" which only incites those who didn't already get it. She begs good-humoredly, "Oohh, give me a break!"

Another man yells, "Sing, baby, sing," which gets her off the hook.

The younger Altman, his father having retired for the night after the first show, watches from a booth. "Guys are going crazy down there," he says excitedly. "It's amazing. The audience always warms to her personality."

Does it bother him that men in the audience take home souvenir napkins moistened with his wife's perspiration?

"It's all pretty good natured. Nothing goes beyond the bounds of propriety. It doesn't bother me at all. I've never seen a crowd fail. They're always yelling, 'I love you.' Crowds take to her. Some performers are very talented and they can entertain, but the audience doesn't feel close.

"It's a totally different world, isn't it? It's not like Washington."