Early one warm spring evening, D.C. police Sgt. Johnny Hunt gunned the engine of his beat-up, pea-green Chevrolet and eased it onto Alabama Avenue SE, right behind the long black car he had come to know well. Most nights in the last three weeks, he'd been following it all over Washington. The car's driver was a convicted robber who police informers said had been responsible for a large number of burglaries in recent weeks.

That night, Hunt and his men surreptitiously followed their suspect for seven hours across Southeast and Northeast Washington as the man visited friends' apartments and neighborhood bars. Hunt watched the man as he pulled over at intersections, opened the trunk and tried to sell household appliances that Hunt was certain were stolen. The clues Hunt was collecting were all part of an intricate puzzle that he hoped would lead to the arrest of the man driving the big black car.

"You get to know so much about one of these guys that when you finally lock him up, you can just overwhelm him with how much you know about him," said Hunt, as his quarry accelerated on Rhode Island Avenue and he followed suit.

Hunt is a member of the Repeat Offenders Project (ROP), an elite squad of the D.C. police department. According to the Police Foundation, a nonprofit group that researches law enforcement matters, ROP is the only operation of its kind in the country. Instead of investigating specific crimes to arrest whoever committed them, ROP (pronounced rope) concentrates on the criminal. ROP detectives try to identify the most active criminals in Washington, investigating them relentlessly in hopes of arresting them.

"The regular detective studies the case, but we study the man," said Capt. Edward (Caesar) Spurlock, who heads ROP. "We're manhunters."

Spurlock acknowledges that his officers often operate near the borderline between legal and illegal tactics when they go after their targets. Known in the police department for their inventiveness, ROP officers dress in street clothes, study their targets' daily routines and follow them night and day. ROP officials acknowledge they sometimes engage in trickery to arrest their targets.

"I'm very pleased with ROP," said D.C. Police Chief Maurice Turner. "A lot of law enforcement agencies around the country are looking at it. They're very interested in the concept."

Turner said he believes the 62-member ROP unit, housed in the 4th District station on upper Georgia Avenue, is largely responsible for a decrease of almost 12 percent in major crimes in Washington so far this year, compared to the same period last year.

Set up in May 1982 as an experimental program, ROP has made about 700 arrests, 95 percent of them for felonies, police said. Initial statistics show that of the first 177 defendants to be tried, 66 were convicted or pleaded guilty, Spurlock said.

ROP, or something like it, will prove crucial to police departments around the country, Spurlock said, because of the amount of crime committed by repeat offenders. Studies have shown that 80 percent of major crimes in large cities are committed by 10 percent of the felons, according to police science researchers, and that applies in Washington as well.

Finding a way to cope with repeat offenders will be "the penicillin of crime control," said Lawrence Sherman, research director at the Police Foundation. "I think the Washington police are way out in front on this."

"What's important is depriving a repeat offender of another victim," said Spurlock, in a soft South Carolina drawl.

"A heroin addict is an opportunist," he said. "He'll do anything and everything: robbery, burglary, fraud. If I have to take a murderer down on a shoplifting charge, I don't care. Just get him off the street."

But some law enforcement officials are skeptical.

"It's not very cost-effective," said one ranking lawyer in the U.S. Attorney's Office in Washington, who did not want to be identified. "I don't think we have the resources to have seven or eight people following one fence.

"I question the philosophy that you ought to try to get an armed robber on a charge of shoplifting a swimsuit."

ROP's success or failure rests on the degree to which judges take into account the ROP defendants' often-serious criminal records, said the prosecutor, adding that he doubts judges will hand out stiff sentences for minor crimes.

"It's nice ROP is putting the courts into the position of slamming these guys because they're nasty dudes," he said. "But I'd be surprised if they get the results they expect in terms of heavy sentences." ROP detectives say that many of those convicted have received light sentences.

Sherman said "it's not clear who's right" in the disagreement between ROP and some prosecutors over whether it's worthwhile to pursue repeat offenders on small charges. But he cited the case of Al Capone, convicted on relatively minor income tax charges, to buttress ROP's side. "He was a murderer, but you couldn't catch him committing a murder," Sherman said.

The detectives pick targets who they believe are responsible for commiting several crimes--regardless of any previous criminal record--based on information from sources that include other police officers and informers.

When ROP was first set up, its main strategy was to follow repeat offenders until they committed a crime in sight of undercover officers, Spurlock said. But that approach was dropped because it didn't catch criminals. "We couldn't see most of the crimes that were being committed," Spurlock said.

Now, if they fail during surveillance to catch an alleged fence buying stolen property, for example, they might infiltrate his circle of friends, sending in an undercover detective to offer to sell property to the fence. The officer then identifies the property as stolen and makes the arrest.

ROP sends its women officers to approach targets at bus stops or in bars trying to glean information that might lead to an arrest, and sends male officers to approach the targets' girlfriends, Spurlock said.

One typical case was the arrest of Arthur Miller, 36, of the 1400 block of W Street NW. ROP detectives decided to follow Miller, who had been charged in the past with 98 crimes and convicted on charges such as burglary and assault with a deadly weapon, because of reports that Miller was engaging in street crimes.

Last July, ROP officers spent a night tailing Miller in the Dupont Circle area as he peered into locked cars, officers said. As detectives approached him, he dropped a straight razor, officers said, and they arrested him for carrying a dangerous weapon. In searching him they found marijuana and charged him with possession. Miller pleaded guilty to the drug and weapons charges, and was sentenced to three years in prison, ROP officers said.

Because of recent court decisions prohibiting police entrapment, ROP officers choose their targets carefully, Spurlock said. ROP officers must be convinced a suspect is currently committing crimes and are barred from suggesting to the target that he commit crimes, Spurlock said.

"We make sure we use the law to the fullest," Spurlock said. ROP's Lt. Robert Sheaffer said that he tells his officers, "entrapment is a defense" against criminal charges. "It's not illegal. Don't be afraid of it."

Turner and Spurlock said they have not received any complaints of ROP officers violating civil liberties, and area American Civil Liberties Union officials said they have not, either. ACLU officials met with Spurlock and Turner to discuss their concerns when the program began, but left with the belief that the program does not practice entrapment.

"We were satisfied they weren't just picking people randomly off the street," said Arthur Spitzer, local ACLU legal director. "It's not a dragnet sort of operation."

ROP is designed to have the maximum impact on crime by concentrating on the worst offenders, Spurlock said. He thinks that the program will catch on in other police departments because of an efficient use of manpower in a time of tightened municipal budgets.

ROP increases officers' productivity because they gather information from other units, such as robbery, burglary and homicide, which traditionally do not consistently communicate with one another, Spurlock said.

Turner gives ROP high marks for working closely with other law enforcement agencies. Two Prince George's County detectives are assigned full time to work with ROP--unusual in police work--and FBI and Alcohol Tobacco and Firearms officials stop by frequently.

"They're pretty ingenious and inventive," said Susan Martin, a researcher with the Gaithersburg-based Police Foundation who has been studying ROP for six months.

The project is unique, Martin said. A similar experiment, in the Kansas City police department in the 1970s, failed, Martin said. Although they worked in largely black areas, the officers in the project were white, she said. They were also clean-shaven under department rules, and drove standard-issue unmarked police cars, easily recognizable to criminals.

Martin said ROP's successes can be attributed to Spurlock himself, the son of a poor sharecropper. An ex-Marine (he was detailed to the U.S. Embassy in Paris), Spurlock joined the department in 1968, and earned a master's degree in administration and diplomacy from American University.

ROP got its start when D.C. Mayor Marion Barry ordered Turner to transfer 100 police officers from clerical jobs to street jobs, Turner said. Rather than scatter the officers in units throughout the city, Turner wanted maximum impact from one squad, and asked three D.C. police captains each to submit a plan. Spurlock suggested ROP, and Turner approved it for an initial six months. ROP is now on its second six-month extension.

Spurlock was allowed to choose his officers, whom he describes as "the best in the city." They're enthusiastic about him, as well.

"This is real police work," said Detective Charley Orman, a 20-year police veteran who used to work in the morals squad. "I always wanted a chance to pursue these people, but I never had the chance to do it right." Orman said ROP differs from "the paper chase downtown."

Spurlock said one reason he's popular with his squad is that he tries to relieve them of the paperwork, and helps them get what aggressive police officers everywhere thrive on: arrests.

"I call it feeding the hungry lions," Spurlock said. "You've got to feed those lions."