Metropolitan area police and department store security guards call her "Jaws"--a convicted shoplifter with 10 known aliases and a knack for using her teeth to bite off the hard plastic sensor devices clamped to expensive clothing.

She was caught on one occasion at a major department store after a sales clerk reported hearing loud crunching noises from her dressing room stall, police accounts show.

Peggy A. Grant, 26, described as 5-feet-11 and weighing 210 pounds, has been arrested for shoplifting at least 13 times since late 1977. She has been convicted on some of the charges, and is awaiting trial in Montgomery County on another shoplifting charge, police records show. Grant declined to talk to a reporter.

Police say Jaws is a professional shoplifter. They estimate that as many as 40 to 100 pros target major department stores and suburban shopping malls on a daily basis. They frequently work in organized teams and many dispose of their hauls through fences in downtown D.C., police investigators say. Police say they believe most professional shoplifters are junkies who sell stolen merchandise to support expensive drug habits.

In some cases the fences, individuals who buy stolen goods to resell to friends or legitimate businesses, place orders with shoplifters for specific items--pants in certain sizes and suits in specified colors. Others operate from the back rooms of pool halls or the trunks of automobiles, taking anything shoplifters can supply.

"It's a multimillion-dollar business," said Capt. Edward J. Spurlock, supervisor of the D.C. Police Department's Repeat Offenders Unit, which tracks professional shoplifters and their fences.

In the case of shoplifters, crime frequently pays, according to Spurlock and other law enforcement officials.

"There is very little incentive for them to stop," Spurlock said. "There's almost no chance of shoplifters being caught once they get out of the store. Unless you get their automobile tag number, they're home free. And if they are caught, very few do any time. Before they go to jail they've got to have multiple offenses--they've got to be known in the courts."

One 24-year-old man, introduced to a reporter by a plainclothes police officer familiar with downtown D.C. fencing operations, said he hits major suburban shopping centers "four out of the six shopping days every week."

"I do it for money for drugs," he said. "I make about $50-$150 a day." In the 18 months he has been shoplifting on an almost daily basis, the man said he has been arrested twice, both times in Arlington. He said he was placed on probation the first time and received a suspended two-year jail term for the second offense.

Law enforcement officials say it is even more difficult to apprehend and prosecute fences--the backbone of the professional shoplifting business.

"We have no doubt there are stores continuously being stocked with stolen goods," Spurlock said. "There's no other way that much stuff could get out of here."

"We've raided pool halls, barbershops and funeral homes," said D.C. police Sgt. William C. Rollins, an investigator. "You find a lot of legitimate small businessmen running fencing operations in the city . . . . You'll walk into these liquor stores and see stacks of blue jeans for sale. We know the stuff is stolen, but we can't prove it. Of course they shop owners don't have receipts to show where they bought it."

Police officers in the District's Repeat Offenders Unit say they have confiscated more than $1 million in stolen goods from fencing operations--many of them fed by shoplifters--in the city during the past year.

But police say that figure is only a small fraction of the estimated millions of dollars that area department stores lose each year to thieves. "Usually when a pro takes stuff, you'll never know it's gone," Spurlock said.

Officials for Woodward & Lothrop recently estimated in published reports that their 16 District area stores alone lost $4.5 million in merchandise to theft last year. The Greater Washington Board of Trade, which contends that shoplifting losses total almost $500 million a year in the metropolitan area, estimates that only a small percentage of the shoplifters are professionals and that the majority are amateur, one-time thieves who steal for themselves.

Police say that the cases they consider most important are the professionals who steal repeatedly.

What police describe as one of the biggest recent raids of a suspected fencing operation was conducted last August when officers arrested a federal government worker after they discovered $100,000 in allegedly stolen clothes and other items in the basement of a town house in Northwest Washington. The items had tags from almost every major department store in the Washington area, police said.

"It looked like a department store in there," said one investigator involved in the arrests. Police allege that the arrested man brought people in and showed them racks of allegedly stolen clothes. The investigator alleged that customers "could put the stuff on layaway or buy it outright."

Police describe other suspected fencing operations they have raided in the past year: a weather-beaten school bus parked near 9th and V Streets that allegedly had been used by fences for collecting stolen clothing for months; a beauty parlor in the 14th Street area with regular customers receiving haircuts in the front room that allegedly doubled as an outlet for special customers who bought stolen clothes in a back room; a 14th Street nightclub with a strip show on the first floor that allegedly stocked a second-floor room with stolen fur coats.

While clothing fences may vary in their methods of operation, police say they believe the majority rely on "boosters"--professional shoplifters so named because of their technique of stuffing or "boosting" stolen clothes in girdles, bulky overcoats or support hosiery.

Many professional shoplifters operate in groups, with two to four individuals who do the actual stealing. They use drivers--usually male--who wait outside department stores while the others fan out to raid the clothing racks.

"We call it snatch and grab," Rollins said. "They grab eight pairs of blue jeans and they're out the door."

As for the drivers: "One guy told me he gets $150 a day doing nothing but driving groups of shoplifters," Rollins said.

Most of the drivers, however, are also the shoplifters' middlemen, who transfer stolen items to fences.

Other shoplifters work independently. A District police informant told police that one of his acquaintances "takes out a panel truck and doesn't stop until he gets $10,000 worth of merchandise." Those shoplifters tend to deal directly with their fences for cash payoffs--usually 20 to 30 percent of the sales-tag price.

Still others have no established patterns for disposing of the merchandise. They steal randomly and sell the items to anyone. A primary target area for shoplifters seeking a fence is a rundown area bounded by 7th and 9th and T and U Streets in the District, police said.

"That's the hub of nearly everything that goes on in the city as far as thieves, burglars, shoplifters and junkies," Rollins said. "Sooner or later they go to that area. Shoplifters can just transfer their stuff from their car to the fence's car."

Another hotbed of fencing operations is narrow, littered Wiltberger Street in the same downtown area, police say. And even though police publicized a raid last summer at a Wiltberger Street town house, an informant recently told investigators, "Wiltberger is known all over the city as the best place still to go to fence stolen goods . . . . If anything they are stronger than before the raid," police reports show. Police say investigations show that fencing operations are continuing on the street.

Although most major fencing operations tend to be concentrated in downtown D.C. areas, police say pockets of related crime have been discovered in suburban towns.

Despite police investigations that show widespread fencing operations, particularly in some locations in the District, law enforcement officials say shoplifters and fences are difficult to track and prosecutors say they are even tougher to convict. As a result, a large percentage of the cases are never brought to court or may be settled through pleas to lesser charges, prosecutors and police say.

"It's hard to make fencing cases," said an assistant U.S. attorney who handles felony cases in D.C. Superior Court. "You have to have specific evidence of them dealing in stolen goods . . . and frequently your only witnesses are thieves themselves."

Prosecutors say a new D.C. law governing trafficking of stolen goods is expected to aid them in building more successful cases against fences. The new law requires only that police have a reasonable suspicion that merchandise may be stolen in order to arrest a suspected fence. The old law required positive proof that the items had been stolen--a requirement virtually impossible to meet, prosecutors say, unless an undercover policeman witnessed both the theft of the items and the sale by the fence.

The rapid turnover of stolen items--particularly clothes--makes fencing operations and shoplifting rings even more difficult to trace, police say.

D.C. investigative Lt. Robert Sheaffer cites another problem: "The police in this area downtown have their hands full with robberies, rapes and homicides . . . . Fencing is a low priority that takes a lot of investigation."

Police say they are also hampered by the number of jurisdictional boundaries shoplifters cross as they circle the Beltway. Late last year Montgomery County police were chasing a shoplifter who drove across the District line. They attempted to summon District police to pick up the chase and became bogged down in red tape, Spurlock said.

"No one knew who to call," Spurlock said. "By the time they got things straightened out, he had gotten away. When they cross a jurisdiction, nobody will follow."

When they are arrested, shoplifters frequently hide their records in a maze of false names and misinformation, police say. If convicted they seldom serve long sentences because court systems in one jurisdiction have no record of their offenses in other jurisdictions, police and prosecutors say.

Shoplifters frequently rely on stolen identification to help establish their trail of false names in the court systems, police and prosecutors say.

"A typical professional shoplifter has been in and out of the court system eight to 10 times," Spurlock said. "They have one or two cases pending in any jurisdiction under assumed names at any given time. If they go to trial they get their time suspended and serve no time and they're back out on the street hitting stores."