LOS ANGELES -- After half a lifetime of dinner theater, regional Shakespeare, light musicals and odd jobs, Larry Drake had been given a part much of the nation may never forget.

At 38, he was a very good character actor with enough work at places like the Old Globe Theatre in San Diego to pay the rent on his four-room duplex in Echo Park. He had never been good at hustling movie and television parts and felt no aching hunger for fame and fortune. He cared about his friends and his work, books, baseball and old movies, and that was about it.

But this particular part -- the role of an office messenger named Benny Stulwicz on "L.A. Law" -- was special and he wanted it to work.

Stulwicz is mentally retarded. He is someone who laughs and cries and thinks and desires and dreams like anyone else, but does it at a slower speed, with some of the hard edges missing, a 45 record occasionally playing at 33 1/3.

Drake wanted to get it right. He went off to talk to experts and eventually found one generous and thoughtful man, 28-year-old Jeff Miller of Malibu, who had many of the secrets of Benny Stulwicz locked inside him.

The results, seen in a succession of "L.A. Law" episodes over the last few weeks (the show airs Thursdays at 10 on Channel 4), have rocked American television and marked what may be the beginning of the end of a stereotype hampering the lives of more than 6 million Americans with similar disabilities.

Drake's sensitive, unconventional portrayal of a man facing the death of his mother and his own sexual awakening has riveted viewers just as the drama of the high-rise law firm is scoring the highest ratings in its two-year history.

What began as just an interesting, one-shot part to provide a case for the fictional firm's novice attorney has now become a recurring role, its life limited only by the imaginations of "L.A. Law's" award-winning writers: Benny has formed a friendship with Arnie Becker, the firm's slippery divorce lawyer; has been charged with sexual assault and exonerated; and last week was told some of the facts of life by another of the firm's attorneys.

The impact on Drake's hitherto successful but little-known acting career is hard to predict, but he is savoring the moment, particularly the question that is invariably asked of producers, writers, hairdressers, reporters or anyone else who might have any connection to "L.A. Law": "Is that actor really retarded?"

"It is the question du jour," says Scott Goldstein, one of the show's producers. "What Larry does is thread the needle between what is real and what is fiction, and that is no mean feat."

Drake's speech, hair style, dress and manner are so different from his character's that it is difficult to match the two of them at first, but he is now recognized in public -- even if few people know his real name -- and he hears, although always secondhand, the question of the day.

"They never ask me, 'Are you really retarded?' because when they see me they have a little more information," he says. "They either see me smoking or driving a car or doing other un-Benny things."

He says he considers the doubts about his own mental capacity "a wonderful compliment. It means I fooled them and that's my job. It means they bought it."

Liz Moore, spokeswoman for the 160,000-member Association for Retarded Citizens of the United States, says: "We are thrilled with the character. We are really excited. A lot of shows will do a one-shot treatment of a character for one episode, but 'L.A. Law' has really made a commitment to this."

The association, a conservative group that has not been happy with mass media handling of retardation in the past, has decided after a great deal of discussion to present "L.A. Law" an official commendation during its California state convention in February.

And viewers who have wondered so long about Larry Drake's own background will have a new puzzle to decipher next month. Heidi Hennessey, a San Francisco woman who has some mental retardation, will play Ivy, Stulwicz's first romantic partner, in an episode scheduled for Feb. 18.

"My fear was that it was going to seem like apples and oranges," Drake says, but Hennessey had been on stage and on television before, and a look at the film afterward confirmed "that it worked very well."

Larry Drake grew up the second of three sons in Tulsa. His father was a draftsman in the oil industry, his mother a housewife. In high school Drake was as tall as he is now, 6 feet 3, and although not quite the hulking, nearly 300-pound figure he would become, he was encouraged to play football. But the high-top shoes blistered his ankles.

"I was always the slowest guy on the team and I remember doing the 100-yard dash one day and pulling a groin muscle and going ass over teakettle and landed on my back with one leg straight up in the air and unable to move it and thinking to myself that maybe it's time to quit."

He fared better as the class wit and one of its most promising actors. His grades were good. His father, obsessed with the fact that no one in the family had ever graduated from college, sent him in 1967 to the University of Oklahoma.

After a disastrous freshman year spent sleeping late, socializing and nursing the shock of failing to interest any fraternities, Drake dropped out to work at a gas station and acquire the smoking habit that torments him to this day. After a spur-of-the-moment trip to the Appalachian Trail that he says he took to think things over, he returned to the university and began to take acting seriously.

Two instructors from Yale, Charles C. Suggs and Robert Greenwood, showed him he had the talent to find new depths in parts he assumed he could do in his sleep, such as Jud Fry in "Oklahoma!" By 1971, while he was slowly completing his degree, he earned his room and board by acting in dinner theaters, living in rooms behind the stage. In 1974 he moved to Dallas and appeared in scores of productions there and on road tours into the Midwest and South.

By 1980 he was deep into "my 30-year-old crisis.

"My girlfriend had left, the lease was up on my apartment, and I had no money left in the bank, and my family was falling apart and going crazy," he says. He decided to move to California. Los Angeles seemed not so different from Tulsa and Dallas and he considered himself too experienced, and too weak in musicals, to compete with the hordes of golden-throated young actors crowding auditions in New York.

He had a silver Honda Civic and a small apartment in Hollywood, but for more than a year could find no one who would pay him to act. He loaded trucks, checked accountants' figures, typed student loan forms and checked automobiles coming off ships.

A part in a 1982 television film, "Dark Night of the Scarecrow," came his way. He played a mentally retarded man who is falsely accused of molesting a little girl and is gunned down by angry citizens of his small town. By the end of the first half-hour his character is dead. The ghost who wreaked vengeance for the rest of the movie was played by another actor.

About that time, producers at the Old Globe in San Diego discovered Drake's versatility -- he won an award for playing seven different roles, including two women, in "Greater Tuna." Soon he was spending more than half the year in San Diego performing Shakespeare and other repertory standards. A steadily employed regional theater actor earns about as much as a public school teacher, but it was enough so that Drake could forget about odd jobs and enjoy his friends and other interests.

His close friend Charles Edward Pogue, screenwriter for "The Fly" and "Psycho III," found himself drawn to Drake as someone "who's got a brain and can sit down and talk to you about things outside this business, which gets a bit incestuous." Both men enjoyed books and old movies, particularly the stylish classics of the 1930s.

They talked into the early morning about their craft and other subjects. Drake spun pet theories, such as his view that the stage was like his favorite spectator sport, baseball, a constant improvisation, while film had a regimented game plan, like football.

Pogue, an actor when they first met in Dallas, now writes full time; Drake speaks of writing as the only part of the entertainment business that might take him away from acting. A play they wrote together, a mystery-comedy called "Whodunnit, Darling," was performed recently in Manassas, Va.

At the Old Globe, Drake played the slow-witted Lennie in Steinbeck's "Of Mice and Men." To prepare, he had visited a center for the mentally retarded in San Diego -- which his agent remembered when "L.A. Law" announced auditions for the part of Benny Stulwicz.

Drake stood out, almost immediately. "A lot of people tried to play this over the top," Goldstein says. "They played to all the cliche's ... It was too much." Drake seemed to sense the limits and yet could convey the character's feelings in a way television audiences could understand. After his appearance as Benny, falsely accused of robbery, the assembled producers and writers began to think out loud about bringing him back.

It was not unusual to have a retarded character make a brief appearance on national television. A more extended role would break new ground, which is precisely what executive producer Steven Bochco wanted to do every chance he got. Terry Louise Fisher, one of the creators of "L.A. Law," had a relative who was retarded and saw the possibilities.

One person close to the program said Drake himself had made a brief pitch for Benny after his initial appearance. He told one producer that both mentally retarded men he had played before had been killed off before the final curtain. What happened to such people in real life who did not die, but had to handle the deaths of their parents, their urge to marry and their need for work?

Drake declined to comment on his own role in pushing Benny but says, "What's wonderful about those people over there is they love your two cents' worth. They don't always pay attention to it, but they want to hear it."

What happened next remains hidden within the murky reaches of "L.A. Law's" creative brain trust. Fisher has left the show in a bitter dispute over salary and could not be reached for comment. Goldstein says he isn't sure precisely who pushed for Benny's enlarged role, but the idea seemed right for a show that lives by vivid incongruities.

Stulwicz's friendly innocence "contrasted nicely with all these fast-track lawyers," Goldstein says. Giving Stulwicz a job as a messenger showed that such people could be valuable assets in the work place -- a facet of the character that delighted professionals in the mental retardation field.

First, though, Drake had to get the character right. Someone on the show staff had given him the name of a Beverly Hills marriage and family counselor, Nora Baladerian. He called and they talked, her initial skepticism flaking off in small bits. He remembers that an initial attempt at a joke -- "So, do their mouths hang open a lot?" -- did not go over well, but Baladerian began to grasp that this was not an ordinary actor.

"I was pleased that he was interested enough in making an accurate portrayal to seek consultation," she says. "The other thing I was surprised by, he was willing to discuss philosophy and a lot of technical background."

Finally, she told him she had a friend. Would Drake like to meet someone like Benny?

Thus Larry Drake came to know Jeff Miller, a 28-year-old man who calls himself a "slow learner," lives in a Malibu board-and-care home and works in a factory packaging clothes for toddlers.

"I had a fair amount of sympathy and empathy and concern for these people," Drake recalls, "but even I had my biases, which I had to dump because of meeting with Jeff ... If I had not had previous information it would have taken me a little while to figure out that there was something wrong at all."

Eating lunch with Drake and Baladerian in a delicatessen on Beverly Boulevard, Miller was "not doing anything much different. He's a little slower getting the mayonnaise off his chin. He peels the paper off a straw like it was a hard-boiled egg ... When you asked him questions you'd realize he'd be slower with his answer, but he was very wide open about what his problem was." Miller joked with both of them, and soon he and Drake were friends.

"I was nervous at first," Miller says, "but he and I opened up pretty soon and I told him where I lived and what I did."

Before long, Miller had talked his way onto the set during the filming of this season's Christmas show. He had wanted to meet Susan Dey, who plays a cool, attractive and committed prosecutor.

"Within five minutes, they met," Drake says. "He got her autograph and they were talking about 'The Partridge Family.' "

Miller lobbied Drake to get him on the show, but "I told him I didn't want to deal with that." Undaunted, Miller approached a few other people, who readily agreed. They put him in a delivery uniform, Drake gave him a few stage directions for handling a pen and clipboard, and Miller's first stint as a television extra went flawlessly.

Drake wrote several pages of notes on what he had learned from Miller and Baladerian. William Finkelstein and Jacob Epstein, two of the series' writers, had further chats with Baladerian. It is their dialogue, Drake says, that makes the character work.

Stulwicz has also proved invaluable in illuminating other series characters, particularly divorce lawyer Becker, played by Corbin Bernsen. In a recent episode, Stulwicz rejected Becker's efforts to remake his wardrobe. The incident revealed how much more self-confidence the messenger had than the suave attorney, even while both faced identity crises.

Most forms of mental retardation are difficult to diagnose, but Drake has worked out his own idea of what happened to Stulwicz, based on the experience of a friend's relative. During a difficult labor, Drake envisages, the oxygen supply to the infant Stulwicz was temporarily cut off because the doctor, wanting to finish his golf game, had ordered a too heavy dosage of a labor-suppressing drug.

Drake sees the character developing new friends and new talents, something that has impressed Baladerian -- who rarely watches television -- about the few "L.A. Law" episodes she has seen.

Miller sees Benny as someone very much like himself, just a guy with a learning problem. "For weeks he wanted to say I was playing him on television," Drake says, "and I kept trying to correct that." Miller says he has checked with several friends with developmental disabilities and they all like the character, "so I think Larry is doing real good."

"People keep asking me how old Benny is mentally and I say it depends on what he is doing," Drake says. He is sitting and smoking in the Echo Park duplex, a small place with two tidy front rooms and two sloppy back ones where the walls are decorated with pictures of Drake in various stage roles. A picture of King Kong is mixed with the others -- a reference to what some have called Drake's gorilla-like physique and an ironic note, given a recent episode in which Stulwicz faced his own sexual problems through his fascination with gorillas at the Los Angeles Zoo.

"Benny is 4 years old socially. He's just not been out yet. But he files better than some 40-year-olds I know."

Playing the part means getting to "the simpler part of yourself and the child part in you," Drake says. "I think this is the reason this is getting to be such a big deal and people warm up to Benny so much. It is the childlike qualities ... no, the unedited part of ourselves is a better way to say it. The unstructured part of ourselves."