HILL AND RENKO case the joint. They rearrange the furniture, they poke at the potted plants, they play with the toys. It's a tiny room they easily overwhelm with sheer bravado, the bravado of two guys thriving in the best of available worlds. They are the kings of the hill: Michael Warren, who plays Officer Bobby Hill, and Charles Haid, who plays Officer Andy Renko, the two most popular characters on NBC's "Hill Street Blues," the best weekly entertainment series on network television.

They can swagger as few TV actors can; not only are they in a hit, but in an honorable hit, the kind networks hardly ever have. They're radiant, like kids who are proud of their parents, or the members of a particularly celebrated fraternity. Tonight, after weeks and weeks of reruns, "Hill Street Blues" returns, in honor of the May Nielsen "sweeps" period, with the first of three new episodes; the last new one will air Thursday, May 12. As the show's fans know, Capt. Frank Furillo (Daniel J. Travanti) and public defender Joyce Davenport (Veronica Hamel) were married in the last new episode shown, on March 3. Tonight will find them troubled newlyweds.

As the season ends, Hill's car will be towed away; Renko will have to work with "Bad Sal" Benedetto (Dennis Franz), a narc who thrashed him in an alley earlier this season; ex-wife Fay Furillo (Barbara Bosson) will turn blue when she hears Frank Jr. calling Joyce "Mommy"; the city will go momentarily broke and pay its police with promissory vouchers instead of checks; and Johnny LaRue (Kiel Martin) will try to win a precinct pool in which the cops guess which human organ a deranged killer will deliver to the Hill Street Station next. Also, Howard Hunter (James B. Sikking) gets to play with a new remote-control surveillance robot.

What characters, what scripts, what a show. It's the epitome of a breakthrough, a living legend. But Haid and Warren can remember that grim first year, when "Hill Street Blues" was a critical success only, and what good is critical success in television? Haid and Warren never doubted the show was good, but they doubted it would last.

"I think that television is a business," says Warren, risking absolutely no disagreement. "And somewhere, a long time ago, they found that it was easier to sell a Ford and a Chevrolet by having people laugh, number one, than it was by having people cry. Number two, it's easier to sell those products by having a car crash and having the driver say, 'Wooo-heee!' and walk away than having the driver taken away in an ambulance. The history of television has shown that quality in dramatic formats does not sell very easily. 'Hill Street' came along at the best of times. Had we been a year, two years earlier, we would have been canceled, without a doubt. I think we came along when NBC had tried everything else and had no choice but to try this."

"Also," says Haid, not as tubby or burly in person as on the show, "even though we did not have the Nielsen numbers at first, we had the advertising numbers. The spending power of the people who watched our show was incredibly high. The people who watched our show were basically those who said, 'I never watch TV, but I watch your show.' " Spinning Off

In the original "Hill Street" pilot, Officer Renko was killed in a chilling final scene. But NBC executives could see Hill and Renko made an ideal team--the sensitive, patient young black man and his impetuous, blue-collar, rednecky pal--and so the ending was revised and Haid agreed to stay on for the series. He isn't sorry. He'd been in a few good movies, like "Altered States" and "Who'll Stop the Rain?," and bad ones, like "KGOD" ("a terrible stinker," says he), and though his agent told him not to take it, he joined "Hill Street" anyway. Warren, a two-time all-America college basketball star, had appeared in such ignoble film duds as "Norman, Is That You?" (playing the gay son of Redd Foxx, yet), so for him "Hill Street" was The Great Opportunity.

Haid is from Palo Alto and divorced and says that, like Renko, whom he calls "a silly fool," he has a bad temper. Warren is from South Bend, Ind., is married and has two young children, a son and a daughter, and says of Officer Hill that he's a "confused" man and "definitely, a part of me."

So popular are their two characters that for a long time there was serious talk at NBC of spinning them off into their own program, "Hill and Renko." In the end, cooler heads prevailed, and NBC defied the old TV tradition of milking a hit to death by building additional shows around some of its characters. "We heard a lot of talk," says Warren, who in person as on the air can lay claim to the title of the handsomest man in television. "I never heard anything concrete. I think those two characters are so important to 'Hill Street' that they wouldn't ever, at this particular time, take us out. In, say, five years, maybe--to make some more money."

"Too late, now," murmurs Haid. "I think we have different opinions about it. I would like to work with Michael. Michael would probably like to work with me. But I wouldn't want to put myself in the hands of some writers I didn't know. I wouldn't do that for all the money in the world." Haid doesn't need money anyway. He was one of the original producers of and is a part-owner of the rights to "Godspell," one of those plays that are being performed somewhere in the world every minute of every day.

"It depends on what circumstances they would put us in," continues Warren, sounding not quite as opposed to the idea as Haid is. "That would be the key. That, plus how much money they're going to pay us to do it. Laughs . We were both very excited about spinning off initially, but neither one of us would have ever considered doing it if we hadn't had it written into a contract that if this did not work, then we knew where we were going to go: back to the Hill."

The success of "Hill Street" does not seem to have bolstered their faith in television. Haid, who spent a month or two last summer meditating with a girlfriend on a hill in India, says gaining "creative control" of the spinoff does not appeal to him. "I don't want even to begin to try to control the quality of a medium that is as sticky and slimy as television," he growls. "I'd be very reluctant to get up there on the same soapbox that all these people get up on every year. I'm a little tired of hearing Robert Blake and Robert Urich and Robert this all get up and talk about 'I want to have this and this.' It's so sad. Especially when their shows are in trouble."

Haid continues on in this vein for a while but doesn't make much sense. However, he is direct in stating that imitations of "Hill Street Blues," such as "St. Elsewhere" (both produced by MTM and both on NBC) do not constitute flattery to him. " 'Mount St. Elsewhere,' that's what I call it. It's the 'La Traviata' of television. I mean, it's the slowest thing I've ever seen in my life, with some terrific actors. But every one of them is a clone of a 'Hill Street Blues' character."

Warren rushes in with diplomatic balm. "But you can't blame them for trying to cash in," he says, as Haid slides back from the edge of the chair, his official harangue position. Warren does concede that "there's no way they can create the same kind of magic." MTM's "St. Elsewhere"--which everyone calls " 'Hill Street' in a hospital," to the consternation of its producers--has abysmal ratings but an outside chance of being picked up for next season (NBC will decide by May 10). That's because another project by Steven Bochco, the Mister Brilliant Young Genius who created "Hill Street" with former partner Michael Kozoll, apparently won't be ready for next fall as expected.

Warren and Haid had come to Washington to appear as guest stars at an auto show. On the phone talking to a public relations woman for the show, Haid is asked if he and Warren will pose for photos. He says, "As long as you make it very clear to them that we will not appear in any photographs or do any interviews with Penthouse Pets or Playgirl cover boys. And I mean that." After he hangs up, he says, "To call a woman a 'pet' is degrading to say the least." The Boil

Neither Warren nor Haid maintains that "Hill Street Blues" is perfect. Warren especially. He is miffed that the writers can't come up with a satisfactory relationship for Bobby Hill to have with a woman. "That's something that needs to be explored," he says, now sliding to the edge of his seat, but talking softly. "I'm not exactly sure why they haven't. Maybe they don't know how to write a serious relationship for a black couple. There are no black writers on the show. They say they were unable to find any.

"Our show, without a doubt, probably hires more minorities over a year's run than any other show. What I would like to see our show do is get into more realistic portrayals. More of a balance. Right now, because we are talking about inner-city areas, the crime aspect is accentuated on our program and most of the so-called criminals are black. And a lot of the victims are white. And the heroes are the police. I would like to see some of the heroes from the community spring up. I don't want appeasement. I would like to see some reality."

Instead of a girlfriend, they gave Officer Hill a boil on his rear end in the early episodes of the season. Warren says this came about purely because Bochco had himself suffered such an impudence while in London last year.

Both actors praise Bochco's "open-door policy." When they aren't playing whiffle ball in the hallway, thereby knocking holes in its drab walls, actors and writers meet in Bochco's surprisingly shabby office at CBS Studio Center (in, shudder, The Valley, over the hills from Hollywood), where the show is made. And they fight. They fight good. "The thing we usually argue about on the show is content," says Haid. "The way things are done, about character, about whether the show's good enough. There are a lot of fights about if it's good enough."

Good enough? Good enough? Doesn't he mean great enough? "We really do aim very high. Sometimes we don't get there at all and other times we completely surpass ourselves," Haid says. If one hangs around for a while with Haid and Warren, or with Bochco, one detects a distinct lack of pretentiousness, perhaps because, for all the hurrahs, they all know that, to a degree, their success can be traced to luck. Bochco, sitting in his office and talking about the show as the season began last fall, said it came about "in great part because NBC had such a need for programs that they made us certain guarantees that are almost never given."

One of those was that the network censor would, as much as possible, keep his grubby mitts off. "We demanded a set of broadcast standards that was different for us than for other shows and--God help us, we'll all get in trouble for my saying this--they gave it to us." The program is sexier and more violent than most TV shows, but it's so genuinely adult that NBC suffers little if any complaint from viewers about the violence or the sex.

Bochco was asked the perennial question, "In what city is 'Hill Street Blues' supposed to be happening?," and he said, "Chicago, Pittsburgh, New York, Newark," like a train conductor. "It's just an amalgam of a lot of cities." The series is shot in L.A., but a second unit shoots some street scenes once a year in Chicago. The Next Group

There was a spell during which the "Hill Street Blues" set was depicted in the press as not such a happy place. Actors were said to be grabbing scripts off the old mimeo and counting their lines, then squawking like jilted lovers if their parts seemed too small to them. Of course every actor's part seems too small to him, maybe even if it's the lead in a one-character soliloquy by Ionesco. Warren, referring again to the dread boil, says, "My character is a real difficult character to write for. I think. You have to really think a long hard time to come up with story lines--I guess, since I haven't gotten that many." Ahem. He also says, "If I don't have something to do in a script, I get pissed off because I think I'm a valuable asset to that show."

And Haid says, for reasons not entirely clear, "The play is the thing to catch the conscience of the king." And: "The one thing that no one will allow is someone to get themselves in some kind of frame of mind that would harm the show. The thing itself. As everybody goes, so goes the show."

"We're all over 30," says Warren. "Though we may not look it. We're all over 30 and we pretty much have in our minds what we want to do, and we know the value of the success. We've all stumbled a lot. I don't think we have any overnight successes on that show. And as a result of that maturity, we have respect for one another."

Haid has a theory. "Last summer, Steven Spielberg's 'E.T.' and some of George Lucas' work and Stallone's work really marked the coming of age of a certain generation of people who've been kicking around for a long time, including Bochco. I've put 'Hill Street Blues' in the same summer, the summer that the business was, in a sense, taken over by the next group. We are the next group. We are the next group of actors, we are the next group of writers, directors, producers, and we're all the same age."

Warren says, "It's a new group, but from my point of view, it seems to still perpetuate the old group's thinking in terms of minorities. It's a new group, but it's some of the same old ideas. And that to me is not exciting. It's frightening." Should Officer Hill become more militant, as he was coaxed to do by black characters in some episodes? "Life is not about being militant. It's about, really, compromises. I think for Hill to come into the 20th century he has got to become more of a human being. Now he's just a real good guy. He's too good. I think he has to have some problems. He's got to have a life. Some conflict."

Another boil, perchance? No, Warren hopes for something better for next season. Haid gets suddenly testy when asked about next year's show: "I think they should throw the whole f------ script out the window and start again next season with something like the same people but just really take some chances." An MTM spokesman says all the regular characters will be back with the show in the fall, but that "we don't know anything about Michael Conrad's situation." Conrad, who plays the philosophical Sgt. Esterhaus, has cancer, but has gone through, the spokesman says, "some very remarkable remissions."

Life, not to mention "Hill Street Blues," would not be the same without the sergeant's reminder at the end of each roll call, "Let's be careful out there." It's practically a hymn.

"Hill Street Blues" is all about what a horrible and wonderful, terrifying and exhilarating place Out There is, and about what it takes to survive in it. Tolerance, mostly, and patience. Television is a horrible and wonderful place, too; when the "Hill Street" cast stormed the stage for its first great slew of Emmys in 1981, there had been nothing quite to match the wonderfulness since "Roots" ignited the American consciousness four years earlier.

Haid and Warren say they will stay with the show as long as it keeps its wits about it. Warren is asked if, upon leaving the show, he would like Hill to die in the line of duty. He says, "To leave is to leave. You die, you die." Haid says to him, "But if you die, they give you a tremendous amount of air time. They give you the entire season! So for God's sake, drop down dead right in front of me."

"We could go into spiritualism," says Warren. "We could chant. You know, it would be very funny, as a matter of fact. The spiritual Bobby Hill comes through your room one night and you're just talking and Belker comes in and finds you talking to yourself. There's a script right there."

"Hill Street" is on its own rarefied wavelength and occasionally dips a tad too low. But it is capable of hitting the highest highs on the air. And then it's just WOW. Like on the Christmas show, when the battling and biting Belker (Bruce Weitz) told the rest of the guys that he couldn't join them for their rowdy Christmas Eve celebration because he had plans--you know, "It's a family time," he said--and one of the last scenes of the show had him sitting alone in his apartment later that night, watching a rerun of "Mr. Magoo's Christmas Carol" on television. The phone rang. It was a wrong number. Before hanging up, Belker said, "Merry Christmas to you, too."

Haid puts his finger on it. "Every once in a while some script will come in and you'll say, 'Holy s---, they did it again! Damn, they did it!" He looks at Warren, who is smiling in concurrence. "That's how we feel about the show."