The Washington region's biggest source of guns that are used in crimes is a drab, two-story brick house that sits along a decaying commercial strip in Prince George's County, according to federal law enforcement data.

Nestled between a pest exterminator and a fast-food joint on Marlboro Pike in Forestville, Realco Guns is a tiny shop that gets crowded if more than three customers show up at once. A half-dozen display cases feature a modest inventory of knives, handguns, rifles and shooting accessories, along with a smattering of literature from the National Rifle Association.

Yet according to data from the U.S. Bureau of Alcohol, Tobacco and Firearms, Realco was the source of 493 guns that were used in crimes from 1996 through 1998, more than double the number of crime guns that were traced to any other dealer in the region.

The weapons most frequently traced to Realco are Davis .380-caliber and Hi-Point 9mm semiautomatic pistols, along with Chinese-made SKS 7.62mm semiautomatic rifles, law enforcement officials said. The Davis .380-caliber retails for about $100, and the Hi-Point 9mm sells for $125 to $150.

Davis .380-caliber pistols are especially popular among young criminals in the District. A 1999 ATF study of crime guns recovered in Washington found that it was the gun most frequently recovered in connection with crimes committed by people younger than 25.

ATF tracing records show also that the guns from Realco are used in crimes relatively soon after they leave the shop. In 1997, about three-quarters of crime guns that were traced to Realco had been sold by the store within the previous three years. Researchers believe that such a fast turnaround from legal purchase to use in a crime is an indicator of potential firearms trafficking.

Realco's owner, Greg del Real, of Rockville, said he steadfastly obeys all laws governing the sale of firearms and goes beyond legal requirements to discourage the flow of weapons to criminals. He would not say how many guns his business sells in a year.

Federal, state and local officials said Realco has not been prosecuted or cited for any violations.

But Realco's track record of supplying guns that later end up in the hands of criminals has attracted the attention of law enforcement agencies that investigate gun trafficking. Others are questioning whether gun dealers like Realco should be more vigilant about where their lethal products might go after they leave the store.

This week, Sen. Charles E. Schumer (D-N.Y.) released a study showing that 1 percent of the nation's firearms dealers sold nearly half the guns used in crimes last year. The study, based on data on firearms that were traced by the ATF, criticized dealers that were the source of a high number of crime guns and called for a crackdown on "bad apples" that funnel weapons to the black market.

Data show that Realco is among the top 15 gun dealers in the nation that were the source of crime guns from 1996 through 1998.

Del Real and his younger brother, Carlos, who works as a manager at Realco, disputed the results of Schumer's study and the ATF data indicating that the store was the source of 493 crime guns traced from 1996 through 1998.

Waving a sheaf of papers to prove his point, Carlos del Real said store records showed that the ATF had traced only about 360 guns sold by the store since 1990. He acknowledged that his list might be incomplete.

ATF officials declined to comment on Realco or on Schumer's study, although they did not dispute the findings of his report. ATF spokesman Jeffrey Roehm said that of the 200,000 guns traced through his agency last year, the "vast majority" were involved in a crime.

Schumer's study also found that there were 10 gun dealers in Virginia and six in Maryland that sold more than 50 crime guns last year, although the report did not name the businesses.

Among them were an Alexandria dealer that sold 241 guns used in crimes from 1996 through 1998, and a Silver Spring store that sold 121 crime guns during the same period.

Law enforcement sources said there are two businesses in Alexandria that conduct a high volume of gun sales, but neither has been known to violate federal laws. The heads of both of those businesses said the report was not referring to them. Law enforcement sources said the Silver Spring gun dealer referred to in Schumer's report was Atlantic Guns, which has stores in Rockville and Silver Spring.

Atlantic Guns owner Steve Schneider said the ATF was bound to trace some guns back to his stores because the company has been in business for 50 years and is a high-volume dealer.

"The data is being used to make it sound like there's something wrong with the dealers, and nothing could be further from the truth," said Schneider, who is president of the Maryland Licensed Firearms Dealers Association. "We run a very reputable shop, as any law enforcement agency will tell you."

Schumer's study showed that nearly half the guns traced to Realco were used to commit crimes out of state. Law enforcement officials said that was not surprising, given Realco's location less than three miles east of the District, where the sale of handguns is banned.

Realco (REE-al-co) Guns has been in business on Marlboro Pike for more than 25 years. Greg del Real, 56, said he's not surprised that some of his weapons eventually fall into the wrong hands.

"We're next to Washington, D.C., which is a high-crime area," he said. "We're in Prince George's County, which is a high-crime area. More guns get stolen in high-crime areas."

But del Real said it is not his fault. He said his store goes to great lengths to screen its customers and is fastidious about keeping and submitting the proper paperwork for criminal background checks. He said his managers keep a keen eye out for straw purchasers -- customers with clean records who buy guns and immediately hand them over to people not eligible to possess them.

"Occasionally, they will be successful in making a straw purchase, despite everything we do to prevent that," he said in an interview this week. "Every time we suspect we have a straw purchaser in the store, we kick them out. We lose a lot of sales that way. . . . We step all over these people's constitutional rights to prevent these straw purchases."

"The intent of the law is to prevent guns from falling into the wrong hands, and we do everything we can to prevent that from occurring," Carlos del Real said. "I work really hard to abide by all these [regulations]. I would tell Chuck Schumer that he's lucky to have us here enforcing the laws."

Greg del Real said ATF officials spent a week in the store last month to conduct an audit of Realco's firearms sales records but found nothing wrong. "They have never found any fault with our business," he said.

Lt. Jack Simpson, of the Maryland State Police crime-gun enforcement unit, said that Realco may be following the letter of the law but that it could do more to dissuade straw purchasers and other suspicious customers.

"They have the right to refuse a sale, and they ought to start using that right," Simpson said. "They run their business; we don't. For them to turn a blind eye to things that are clearly criminal is a shame.

"They get calls every day from the ATF for a trace, so this isn't a surprise to them by any stretch. This is not a shock to them."

The del Reals estimated that they receive fewer than 10 calls a month from ATF officials attempting to trace guns sold at the store. They also argued that just because the ATF traces a gun doesn't necessarily mean the firearm was used to commit a crime.

The ATF's Roehm said that the bureau looks at the number of traces back to a particular retailer as a potential sign that a dealer is acting illegally, but said "the fact that crime guns come back to a dealer is not a definitive indicator of criminal activity."

ATF agents and other experts cited several reasons a dealer may have many guns traced back to it: a high volume of sales, its location in a neighborhood where guns are common, or its frequent use by straw purchasers.

"It can be a variety of things that have nothing to do with the dealers," said Glenn Pierce, co-director of Northeastern University's Criminal Justice Policy Research Center. Nevertheless, he added, identifying dealers that are the source of many crime guns is a valuable tool to allow the ATF to target certain neighborhoods in its investigations.

Stephen Richards, whose family owns Potomac Arms Corp., Alexandria's largest firearms dealer, located on the waterfront in Old Town, said he doubted his company is the dealer noted in Schumer's report. "If those numbers are correct, it's not us," he said.

Richards said that ATF officials conduct an estimated 30 traces a year on guns that his business has sold, dating back to 1958. The store sells about 1,000 handguns a year, accounting for roughly half its firearms sales, he said.

"There is little doubt in my mind that there are criminal dealers out there who will intentionally sell to non-qualified buyers," Richards said. "I'd like to see them all in prison tomorrow -- they make me look bad. We, Potomac Arms, are extra conservative in our sales. If there's a hint of a straw purchase, we don't make the sale."

David MacGillivray, the president and CEO of Interarms, which is located down the street from Potomac Arms, said he doubted the study was referring to his company. Interams is not a gun dealer, but an importer of firearms, selling to about 25 or 30 wholesalers around the country, he said.

MacGillivray said his business sells a large quantity of firearms -- as many as 200,000 a year at one point, and about half that in recent years -- and that ATF officials routinely conduct traces, as many as 25 or 30 a day. "We follow all the regulations and obey all the laws," he said.

Staff writers Patricia Davis and Barbara Vobejda contributed to this report.

CAPTION: Realco Guns has not been prosecuted or cited for any violations, officials say.