A Northwest Washington man described by federal agents as a major gun supplier to District drug dealers was arrested near Woodbridge yesterday on an arrest warrant after he had purchased a semiautomatic weapon from a gun store, said a spokesman for the local office of the Bureau of Alcohol, Tobacco and Firearms.

The agency identified the man as David Isom, 30, of the 600 block of Irving Street NW.

Isom was arraigned yesterday afternoon at U.S. Magistrate's Court in Alexandria and charged with one count of purchasing a handgun with a false identification, according to a spokeswoman in the U.S. attorney's office in Alexandria. She said he is being held pending a detention hearing on Monday.

Dick Pedersen, a spokesman for the Bureau of Alcohol, Tobacco and Firearms, said Isom had purchased more than two dozen guns, mostly 9 mm semiautomatic handguns, from several stores in Virginia this month. Sale and ownership of handguns are illegal in the District and residents with D.C. identification cannot purchase handguns elsewhere.

"Isom used a false identification to purchase the guns," Pedersen said. "He then took the guns into the city and sold them to members of the Jamaican posses."

Local police and federal authorities have identified Jamaican gangs, known as posses, as violent-prone drug traffickers from New

York and Miami who have turned the illegal cocaine markets in the District and Prince George's County into deadly battlefields.

Nationwide, the posses are responsible for more than 600 homicides in the last two years, according to Jerry Rudden, a spokesman for the national Alcohol, Tobacco and Firearms office. In the District and Prince George's County, officials have connected Jamaican gang members to several drug-related homicides.

Pedersen said the gang members favor semiautomatic 9 mm pistols, particularly a large handgun called a Tec-9. When Isom was arrested yesterday he had just purchased a Tec-9, Pedersen said.

"This guy was a major supplier for the Jamaicans," Pedersen said. "We figure there are several hundred Jamaican posse members in the area and this guy put 30 guns in their hands."

Pedersen said Isom paid about $300 for each of the guns he bought and turned 100 percent profit on each sale. He said local posse members also are bringing in weapons from New York and Miami.

Isom purchased a number of the Tec-9 guns, which resemble a machine pistols with long magazines. "It is a mean-looking gun and the drug dealers love to show off with them," Pedersen said.

Pedersen said agents staked out a Virginia gun store Tuesday where they expected Isom to make a purchase but when he had not shown up at closing time, they left. Shortly afterward, Isom arrived at the store, found it closed, went to another store and purchased a gun, Pedersen said.

Yesterday federal agents followed Isom to a Virginia store again, and arrested him shortly after he had bought a gun, they said.

Michael Bregman, special agent in charge of the Washington office, yesterday applauded Isom's arrest.

"We are continually working with the Metropolitan Police Department and other police agencies concerning the Jamaican problem," he said. "What we have here is a man perpetrating a criminal act to get guns into the hands of other criminals . . . . We consider this a major arrest."

Pedersen said his office has supplied D.C. police with the serial numbers of all the handguns purchased by Isom and they expect those guns to start showing up soon in the District.