PHILADELPHIA — They look like delis or hardware stores — a corner shop decorated with stuffed Easter bunnies, a nondescript brick building in the shadow of Interstate 95, a storefront so picturesque it was featured in the new M. Night Shyamalan movie.

In recent years, the dozen or so federally licensed firearms dealers operating in Philadelphia have done brisk business meeting the demand from legal buyers in one of the nation’s most violent cities. They are also a major source of weapons used illegally, according to a new report that offers a rare glimpse into the link between legal gun sales and criminal activity.

From 2014 to 2020, six small retailers in south and northeast Philadelphia sold more than 11,000 weapons that were later recovered in criminal investigations or confiscated from owners who had obtained them illegally, according to an examination of Pennsylvania firearms tracing data by the gun control group Brady, the most comprehensive analysis of its kind in decades.

The report’s conclusions confirm what law enforcement officials have long known. A small percentage of gun stores — 1.2 percent of the state’s licensed dealers, according to Brady — accounted for 57 percent of firearms that ended up in the hands of criminals through illegal resale or direct purchases by “straw” buyers who turned them over to people barred from owning guns.

That finding was in line with a new batch of tracing data obtained by the House Oversight and Reform Committee, which also found that a small number of retailers in Georgia, Indiana, Florida and Michigan were responsible for a high proportion of so-called crime guns traced by law enforcement, according to a letter the committee sent to the Bureau of Alcohol, Tobacco, Firearms and Explosives on Thursday.

“There is a wide spectrum of behavior we’re dealing with when it comes to these stores,” T. Christian Heyne, Brady’s vice president for policy, said in an interview. “Some of them need support, some need more scrutiny, and some of them just need to be shut down.”

The vast majority of dealers, Mr. Heyne added, “sell guns safely and often exceed the letter of the law.” The purpose of releasing the report, he said, was to pressure federal, state and local officials to focus on countering “the bad actions of a few.”

The House panel’s continuing investigation used data from the A.T.F. to show that “a small number of gun dealers are disproportionately responsible for flooding our streets with guns that are used in crimes,” Representative Carolyn B. Maloney, the New York Democrat who is the chairwoman of the committee, said in a statement.

A.T.F. officials have long argued against making any inferences from crime-gun data in isolation without knowing the percentage of a store’s overall guns end up in the wrong hands. But that information, along with many other details about individual store operations, is not made public.

Twenty years ago, the gun lobby pushed an amendment through Congress preventing the A.T.F. from distributing trace data beyond law enforcement agencies. That means even basic numbers are hard to come by. When Ms. Maloney’s staff requested granular information about dealers with high numbers of crime gun sales, the A.T.F. refused to identify retailers by name — giving each an anonymized numeric label.

Yet the left, which has had little success in restricting access to semiautomatic weapons or expanding background checks, is making incremental progress in rooting out more of the information.

Last year, President Biden commissioned a large-scale national gun trafficking report that will include analyses of gun makers and dealers, the first of its kind in two decades. And some local officials, who are not legally constrained from releasing data, have been compiling data from local law enforcement sources.

In 2019, Pennsylvania’s attorney general, Josh Shapiro, began posting online trace data from 186,000 crime guns reported to the state by local law enforcement officials dating back to 1977. The database did not include the crimes associated with each trace, or the identity of the dealers. But Brady researchers determined the names of retailers from phone numbers listed on the database.

“I have said for years that most crime guns come from a small number of stores,” said Mr. Shapiro, a Democrat who is running for governor. “We need to do more as a state to make it harder for gun sales to lead to gun violence.”

But Mr. Shapiro, echoing the A.T.F., cautioned against drawing too many conclusions about individual sellers, adding that “a small percentage” of bad sales at a busy, but otherwise legally compliant, store could show up as dozens of crime guns. He also emphasized that the information, while useful, was incomplete because many local departments did not contribute tracing information.

Larry Keane, a top official with the National Shooting Sports Foundation, a firearms industry trade association, went even further, accusing gun control activists of trying to “name and shame” honest small-business owners and singling out Brady for compiling misleading lists of “bad-apple” dealers. He cited a 1998 report by the A.T.F., which described gun tracing as a “starting point” for investigators to unravel a defendant’s illegal behavior that “in no way suggests” the dealer’s culpability.

But gun control activists say the Pennsylvania data, however incomplete, points to an inescapable policy conclusion: The A.T.F., an embattled and chronically understaffed agency responsible for overseeing 75,000 licensed dealers, needs to intensify its monitoring and oversight of the most troubled gun sellers.

To that end, the Biden administration has proposed a 13 percent increase to the bureau’s budget, to pay for 140 new agents and 160 new investigators to inspect gun dealers.

The House oversight committee asked the A.T.F. in 2019 for data on gun shops that had received warnings or recommendations that their licenses be pulled, including the name and location of the dealer, the violations identified, the recommendations by the inspector and what steps the bureau took after the inspection.

The A.T.F. has not yet provided that information, which the committee says it needs to complete its investigation, now two and a half years old, into the role that gun dealers play in the epidemic of gun crime.

Ms. Maloney’s committee released its initial analysis of the data that the A.T.F. has provided, which included anonymized dealers, their gun sales and the number of those guns that had been traced back to crimes. It also shared how many of the documented gun crimes occurred within five years after the gun was sold.

The A.T.F. last released a large amount of similar data in 2000.

The bureau gave the committee six years’ worth of anonymized gun trace data for the top five dealers in each state. It also provided anonymized data on gun sales for 12 selected dealers in a handful of states.

The committee found that three dealers sold significantly more crime guns than the others as a percentage of their average monthly gun sales.

Two gun shops in Georgia and Indiana — identified as “GA01” and “IN02” — presented an especially troubling picture: On average, about 10 percent of their monthly guns sold were used in crimes. GA01 sold more than 6,000 crime guns from 2014 to 2019, accounting for more than half of Georgia’s reported guns later recovered at crime scenes. About 7 percent of the monthly guns sold at a Michigan store identified as “MI01” were crime guns, according to the analysis by Ms. Maloney’s committee.

The committee also found that in Puerto Rico, crime guns bought outside the territory all came from Florida, indicating that guns could be moving in predictable corridors between parts of the country.

In July, the Justice Department created five federal strike forces aimed at gun traffickers who flood urban streets with illicit firearms. Attorney General Merrick B. Garland said they would be overseen by U.S. attorneys in New York City, Chicago, Los Angeles, Northern California and Washington, D.C., places identified as end points for significant gun-trafficking corridors.

The situation in Pennsylvania was somewhat different, according to the Brady analysis. Most of the crime guns recovered in Philadelphia, and to a lesser extent Pittsburgh, were sourced from stores inside the state. New York and other cities, by contrast, are often inundated with out-of-state guns.

In Philadelphia, several of the gun shops with the highest number of crime gun traces have already closed, or been shut down, after investigations by the A.T.F. found major problems with their record-keeping or a willful failure to stop the straw buyers.

But some of the retailers still operating in Philadelphia have had similar problems.

While the vast majority of guns recovered in any given year are not linked to violent crimes, 30 weapons originally sourced to Philadelphia dealers were associated with homicides in 2020, according to Brady.

In addition, Philadelphia retailers have also been named in weapons trafficking cases brought by prosecutors in nearby Montgomery County — including a straw-purchasing spree by a man who had just turned 21, and monetized his clean criminal record to buy and sell 36 handguns, according to a criminal complaint filed in 2020.

From 2019 to 2021, three Philadelphia men bought and resold 37 weapons — three of them from Delia’s Gun Shop in the Torresdale section of the city, which was responsible for 2,644 traced guns. They bought three more from Frank’s Gun Shop, a nearby retailer linked to 451 crime guns from 2014 to 2020.

A woman identifying herself as a manager at Delia’s hung up when a reporter called for comment; the owner of Frank’s Gun shop did not immediately return a request for comment.

Glenn Thrush reported from Philadelphia, and Katie Benner from Washington.