What's wrong with this picture? The room is full of cops clutching steaming cups of coffee. As the sergeant with the thinning red hair and the thickening paunch steps up to the front of the room, the cops quiet down. The sergeant begins reviewing the day's operations, anticipating problems and issuing orders. But instead of the usual dismissal, "Let's be careful out there," he signs off, "Let's get out there and do it to them before they do it to us." As Sgt. Stan Jablonski on NBC's Hill Street Blues, Robert Prosky, 53, is applying his own sensibility to the ritual made famous by Michael Conrad, who died of cancer last year. Prosky isn't worried about joining the force late, either. "It's not like I haven't been around," says Prosky. "They know I'm not just a hack walking in."

Indeed, as a crown prince of character actors, Prosky possesses a face you don't forget—and a name you do. The countenance has a panorama of experience on it, which appealed to Hill Street's creators. For Conrad's replacement, no rookie would do. Last season regulars Joe Spano and Betty Thomas were tried. "But what was missing was the quality of an older man who'd been around the track," says co-executive producer Greg Hoblit. "Michael had that, and Bob has that."

Playing another world-weary fellow secured Prosky his post on Hill Street. Last spring, as an over-the-hill real estate salesman in the drama Glengarry Glen Ross, Prosky impressed critics and drew a Tony nomination. That triggered Hill Street's interest. The creators of the series caught Prosky's performance on Broadway. "That just did it," says Hoblit. Conceived as Irish, the sergeant's nationality was changed to that of a Pole to accommodate Prosky.

Although a newcomer to TV, Prosky has been a legend among serious actors for years. In a business notorious for impermanence, he was parked for 23 years at the Arena Stage in Washington, D.C., where he performed about 130 roles. "Bob was sort of a phenomenon," recalls Hill Street's Bruce Weitz, who once played Happy to Prosky's Willy Loman in Death of a Salesman. "I mean, he was the burgomaster of Capitol Hill."

For Prosky stability was a mixed blessing. Although he was quite happy with all the plum parts, "the lack of wider recognition did bother me," he admits. For years he periodically auditioned in New York, but found it costly both in time and money. "Generally speaking, they might take a chance on a lovely young ingenue, but not on a character actor," he says. Then, in 1980, first-time director Michael Mann cast Prosky as an intimidating mobster opposite James Caan in Thief. Prosky suddenly found his star was born.

Moving from stage to films, he turned up in quick succession as gruff, gravel-voiced characters in Monsignore, The Lords of Discipline, Christine and The Natural. The steady work also meant that Prosky seldom saw Hill Street. In fact, after he was cast, he asked the producers to ship him 25 hours of Hill Street tapes.

Though movies appealed to Prosky, TV did not. He had turned down the role of Coach in Cheers. "I've frankly been resisting television," he says.' But he decided to sign a three-year contract for Hill Street. First, "the quality of Hill Street made it attractive," he says. Second, "I have three sons and a wife going to college."

Prosky is also cautious about one consequence of prime time: overeager fans. "I face that with some apprehension," he says. "I think my wife faces it with more." Prosky had a bout with the man on the street when Thief raw on TV while he was doing Glengarry. En route to the theater one night, he emerged from a subway station to confront a 42nd Street habitué who recognized him. "Hey man, you Thief, you Thief," said the fellow loudly. As the actor hurried away, the fan kept hollering. Says Prosky: "The one thing you don't want yelled at you on 42nd Street is Thief! Thief!' "

Acting wasn't always his ambition. The only child of a Philadelphia grocery owner and a housewife, Prosky earned a degree in economics at Temple Univeristy, then joined the Air Force just in time for the Korean war. When his father died, Prosky returned from the service to run the grocery. But after he won a scholarship to acting school in New York, he left his mother minding the store. In 1958, after several years doing off-Broadway shows, the then 28-year-old actor lugged three suitcases down to Washington for an intended eight-week stint at the Arena in The Front Page. Shortly after arriving he met Ida, a journalist (who is now an anthropology graduate student). They were married in 1960 and have three sons: Stefan, 23, John Patrick, 22, and Andrew, 19.

In Los Angeles Prosky is again living out of suitcases—and weathering a transcontinental marriage. Ida, 49, occupies their Capitol Hill town house, while Prosky has rented a small Studio City apartment. "There's no pool, but it does have a Jacuzzi spa in the back," says Prosky. "I've noticed that some interviewers who came here expected more." Prosky vows he will keep disappointing them. Although his income has shot up at least "tenfold" from the $700 a week he made at the Arena, Prosky insists that he's not the sort to take suddenly to wearing pinkie rings and driving a Rolls. "I am not living up to my income," he says proudly. "And I have no plans to."