This is a gilded week for actor Robert Guillaume, whose ballyhooed series, "Benson," debuts tonight on ABC.

Only four days ago, Guillaume received an Emmy Award for "Benson's" forefather, the acerbic butler on "Soap." And his glistening, dour face graces the cover of TV Guide. It's all enough to give a guy a swelled head.

Not him, says a composed Guillaume, not as long as he has this sister back in St. Louis. "She calls and says, 'You're not working at the post office anymore.' For her I was really doing something when I worked at the post office.

"After some convincing that this is honest work, she says, 'Well, do you have your own makeup man?'" says Guillaume, his own gruff voice rising in imitation of her high-pitched disbelief and then softening for her hushed warmth.

"And then she will say, 'well, he really has done a good job with you, 'cause you were ugly when you left here,'" he continued, laughing. "So there is always something very sobering to remind you to take it all in stride."

Robert Guillaume and "Benson" are hot. ABC television has given the comedy the coveted prime-time slot between the two ratings warhorses, "Barney Miller" and "Laverne and Shirley," and, according to ABC, the show was the fastest of the new ones to sell its commercial time, at an admirable clip of $115,000 for 30 seconds.

Undoubtedly this is the peak of an intermittently bright 20-year career, but the 50-year-old Guillaume's response to the sensational predictions is pleased detachment: "Needless to say I'm elated, but it also gives you a lot to live up to."

Underlying this solemn disposition is a frustration, a constant discontent that the best isn't good enough. What Guillaume really covets are the notices and perks of a singing star. He entered show business in the mid-1950s with a portfolio of Caruso, Roy Hamilton and Billy Eckstine and earned most of his credits as a show-tune man in "Golden Boy," "Purlie" and "Guys and Dolls." Singing remains his ideal.

"I have appeared on some Broadway albums but I've always wanted to make it singing, singing as a solo artist. And I thought I would get a chance as a result of getting visibility on the tube," says Guillaume, ruefully. Last winter, when "Benson" was still a rumor, Guillaume, cut a disco single and toured the strobe-light world of big city discos -- but the record didn't fly.

"He had fun pushing the records down the deejays' throats. That was the thrill," says a friend. "But the idea of making a disco record didn't appeal to him. It was a career move. As a singer trained in Catholic and opera traditions, he wants to be serious.

But Guillaume's lingering frustration is not an overriding regret. He likes Benson. In the first episode Benson arrives at his new quarters, the household of a daffy, inept and widowed governor, a relative of his old employer, the Tates of "Soap" infamy. Usually in a spin-off some aspect of upward mobility supplies the story line. Here our man Benson is still our man Benson but the only sign of improvement is that he has fewer white people to worry about.

Sensing raised eyebrows, Guillaume quickly points out the advancement. "It's no longer a apron gig. I run the governor's mansion in an administrative capacity," he explains. Yet, despite its status as a sit-com, a video breed that either overpreaches social values or avoids them, "Benson" will be judged for racial relevance.

"Through my own feisty personality I think I avoided a demeaning stature on 'Soap.' Even though the producers and I had our differences over the years, no one wants this to be a throwback to the 1930s and 1940s images of blacks on the screen," he says.

When the snowy-haired Benson with the quick quip first emerged from behind the swinging door in the Tate household, he was freewheeling, tart, holier-than-thou. Even blacks, who generally championed his sass and admired his lack of eyeball rolling, took objections to some lines, such as Benson explaining why blacks don't have acne: "God said, I won't give them pimples. I'll just screw up their hair."

To all criticism, Guillaume maintained that Benson was a simple man with a strong dose of candor and an equally strong strain of black consciousness."For all black people, I want the character to look as though he's not uptight about prejudiced white people. As long as they know their place, they can have their prejudices. I'm not threatened by every prejudice that occurs. We need that kind of stability as people."

What he is promoting through Benson is a no-frills look at the common man. "Benson," he says, "upgrades the image of the black ordinary working man. He's a character with wit and intelligence, no great ambition, no great philosophy. In this series, he's more complete, more vulnerable. We have not had an opportunity as actors to be ordinary."

And his identification with the common man not only influences his acting but his casual life style. Once married briefly, he has two sons in their early 20s. For the last nine years he has shared housekeeping with Fay Hauser, an outgoing and soft-spoken North Carolina woman, who is an accomplished songwriter (for Sister Sledge) and actress ("Roots II"). When "Soap" first went on the air, the couple lived in chic Laurel Canyon and Guillaume was given to quotes such as, "You gain a measure of respectability when you live beyond your means." But now they share a modest house, sans swimming pool, in Studio City, and have been featured as an "in" couple by People and Essence magazines.

Twenty years younger than Guillaume, Hauser has one major complaint about their relationship -- his ignorance of the art of relaxing. "Everything is work to him . . . Whatever he's doing, he's doing it for keeps," she says.

Guillaume is almost apologetic about his lack of pretense and star style. "I would consider myself laidback but not like the California type. I don't have the right clothes, I don't go to the right restaurants. And I don't have that much need for relaxation because I don't get that uptight at work." He will admit to a few pastimes -- bowling, piano playing, work outs at the gym and movies.

Thought Benson has given him the option to upgrade or downplay his life style, Benson hasn't given him an acting challenge. "In the public's mind, this is the biggest thing I've ever done. But I have done bigger and more demanding roles."

Perhaps the hardest was getting started. The start is hazy but the story can be safely picked up at Guillaume's grandmother's house. Because his father abandoned the family and his mother had a drinking problem, Guillaume recalls, his grandmother applied a strict Catholic morality to her charge, and his three brothers and sisters.

In this rigidity, and poverty, Guillaume found his own strength. "I don't remember them as rough times. In retrospect I know that they must have been rough, but I had a tremendous ability to cover them over," he says, adding he was taught "never to despair and never think we were locked in a corner because of racism." Eventually the pool halls of St. Louis competed with his altar boy and choirboy duties, and the slight, witty youth spent several undirected years in the Army, as a clothing store clerk, streetcar motorman and dishwasher. Often, he'd sing on these jobs. Finally, while he was studying business administration at night, a college voice teacher chaneled his energy, talent and restlessness.

"Leslie Chabay was the first person to say I had potential to sing the classics. My earliest ambitions were to do the airy, boy soprano tunes. Then, after I decided I could make a living at it, I decided on opera. Now because I learned those languages -- German, French and Italian -- I can do 'I Who Have Nothing' in all of them," says Guillaume, laughing.

From the mid-1950s Guillaume was set on a singing and acting course that led eventually to Broadway, raves as the hip preacher in the national tour of "Purlie" and then to his Tony nomination role as Nathan Detroit in the all-black revival of "Guys and Dolls" in 1976. The climb was steady starting at Karamu House, the regional theater in Cleveland, where Oscar Hammerstein heard his debut in "Carousel." Guillaume left his mark on such major productions as Arean Stage's presentation of "No Place to Be Somebody" in 1970, and he also appeared in "Kwaminia," "Othello," "Jacques Brel" and "Porgy and Bess."

Did Guillaume find his challenge?

"Well, I enjoyed 'Purlie.' And I liked 'Detroit,' but it wasn't a challenge. A role has to be original for the challenge. Maybe Johnny Williams from 'No Place.'" What he is searching for are roles that will give him a special identity, as his major influence, Sidney Poitier, has. "My whole thing about Sidney is his melange, the totality. He has a certain cool, a certain economy in his acting, his diversity, his longevity and his growth," says Guillaume.

In every conversation, his craving for something else, usually the singing reputation, surfaces. "I never expected to become well known as an actor, especially a comedy actor. While a few people like my singing, no one seems quite taken by it. And I guess I'm not saddened by that," says Guillaume, his face always managing a trace of cynical melancholy.

"I'm really happy at what's happening."