Six men have been shot to death in the last week in adjoining District neighborhoods and in two disparate sections of Prince George's County in what police call a deadly drug war involving Jamaican gangs that have muscled their way into lucrative Washington area markets.

It is a war for control of the cocaine markets in parts of Bellview in Southwest and Congress Heights in Southeast as well as in suburban Langley Park and Oxon Hill, police said. The gangs, known as posses, are not only fighting it out with local drug dealers but with each other, police said.

Five of the men who died in the last week were identified by police sources as Jamaicans, and the sixth was killed in what police called a "crack house" run by Jamaicans. Most of the men were shot several times and left on the streets.

Violence has always been associated with the drug markets in the area. But it is the execution-style slayings and increased firepower associated with the Jamaican posses that have police and federal authorities concerned. D.C. police said they may consider issuing patrol officers semiautomatic weapons to better protect themselves.

Dick Petersen, spokesman for the local office of the Bureau of Alcohol, Tobacco and Firearms, said, "They think nothing of having a shootout on the street . . . . And they can be very brutal with their own."

While police officials are quick to point out that not all Jamaican nationals in the area are involved in drug trafficking, they do say the posses are made up of Jamaicans who come here from New York and Miami. Some are in the country illegally. Police have identified seven posses operating in the Washington area.

Jamaican gangs figured prominently in several court cases this year involving two housing projects in Northeast Washington near Kenilworth Avenue and Benning Road. At least 20 residents of New York and Miami, many of whom were identified as Jamaican nationals in U.S. District Court records, were arrested in June and July in eight major narcotic distribution cases. At that time, police linked six drug-related homicides to the Jamaican drug dealers.

In District drug markets run by local dealers, it is unusual to find sellers who are armed, said Assistant Police Chief Isaac Fulwood. Only about 10 percent of the local people arrested for drug activity are armed, he said. But of the 71 New Yorkers arrested this year in the police department's 7th District, which includes far Southeast and Southwest, 60 percent were armed, he said.

"We have confiscated guns with silencers and with clips which will hold 100 bullets," he said. "They have heavier firearms than the police carry."

D.C. and Prince George's County police carry .38-caliber six-shot revolvers.

The posses introduced crack, a potent form of cocaine, to the Washington area about 18 months ago, according to police sources. It is a profitable business: A quarter-gram of crack that sells for $10 in New York brings $25 here.

Police say the posses control the crack market here and are trying to take over the District's active cocaine market. No one knows what share of the market Jamaicans control, but it is the struggle for the cocaine market that has led to numerous shootings and an increasing number of homicides, police say.

The number of homicides in the District appears to be on the increase, Fulwood said. So far this year, there have been 190 slayings in the city compared with 196 for all of last year. The 7th District recorded 56 homicides this year.

"A substantial number of those are related to the Jamaican gangs," Fulwood said.

In Prince George's County, police said this year's 83 homicides to date have surpassed last year's total of 52. They expect that the number of homicides for the year will surpass the record of 86 slayings committed in 1982. A police spokesman said the increase this year is attributed to the drug trafficking in the county. He was unable to specify how many of the slayings were related to posses.

D.C. police have identified the man found shot to death on Sunday in the 400 block of Orange Street SE as Mekeim Tyrone Johnson, 21, of Brooklyn, N.Y.

On Saturday, two men were found shot to death in Southwest within a block of each other just before midnight. They have been identified as Alex A. Shim, 21, of Silver Spring, who was found in the 100 block of Danbury Street SW. Around the corner at 4215 Martin Luther King Ave. SW, police found Ludlow A. Collins, 25, of the 1000 block of Columbia Road NW.

Last Thursday, Francisco Sealy, 20, of Brooklyn was found dead of gunshot wounds in the 400 block of Mellon Street SE.

Prince George's police said Arthur Dalvin Vincent, 24, of 7906 14th St., Langley Park, died of multiple gunshot wounds Sunday at a crack house operated by Jamaicans in the 2200 block of Phelps Road, Adelphi. Another man was shot as well but survived.

Last Thursday, Collin Phelmin Branford, 30, of 8137 15th Ave., Langley Park, was killed in front of his wife by two gunmen who entered his apartment. A friend visiting Branford jumped from a window to escape the gunmen. Branford's wife was not injured.

Investigators have been unable to determine the motive for Branford's death but they say it is always difficult to get witnesses to talk about drug-related slayings.

"We don't get many Jamaican informants," one county investigator said. "The way that {Branford} was shot is one reason why."

Nationwide, the Jamaican posses are responsible for 600 homicides in the last two years, according to Jerry Rudden, a spokesman for the national office of the Bureau of Alcohol, Tobacco and Firearms.

"Most of the violence surrounding these guys is comparable to the violence during the Prohibition days, with the ruthlessness and total disregard for life," he said.

The posses, which operate in many of the country's large cities, take their name from American western movies. Born in the ghettos of Kingston, Jamaica, the posses have been traced to the political unrest in Jamaica in the late 1970s, when many residents armed themselves during a fiercely fought election for prime minister.

Several dozen posses are operating in this country. In this area, police sources have identified the Shower, Spangler, Super, Banton, Waterhouse Riverton and Tel-Aviv posses.

A vice officer who has followed the movement of the posses closely said they are masters at forging identifications. New arrivals are routinely supplied with a fake passports, Social Security numbers and driver's licenses.

Fulwood said the ability of gang members to move quickly in the network of the posses from city to city makes it difficult to trace those responsible for shootings and homicides.

Fulwood said posse members often move into a neighborhood with vacant buildings and simply take them over as they have done in parts of Bellview. Or they might pay to use someone's apartment for a few days.

Petersen, of the Alcohol, Tobacco and Firearms bureau, said several of his agents were helping D.C. police with their work in Southeast Washington. They are interested in the guns that the police are seizing.

"The Jamaicans really like the 9 mm semiautomatic guns," Petersen said. "They particularly like the Tech-9, which look like a James Bond gun."

Fulwood said the use of 9 mm semiautomatic guns had become so prevalent that the police department is tracking slayings committed with that type of gun. "More and more 9 mm guns are showing up," he said. "We are looking at all the 9 mm-related murders."

Prince George's County police are also connecting 9 mm weapons with posse activities. On Nov. 6, Ralph Allister Gray, 32, described by police as a Jamaican drug distributor, was shot and stabbed several times near his apartment at 3200 Lassie Ave., Temple Hills. In his apartment police found two 9 mm semiautomatic handguns, a revolver and a empty case for an Uzi submachine gun.

Fulwood said he had committed an average of 40 Special Operations Division officers a day to the 7th District to help local officers. Clean Sweep, the unit he originated a year ago to deal specifically with the growing drug problem in the city, also has targeted the same area.

"Because we have the use of these extra officers, we are able to respond much more quickly to tips involving posse activity," he said.

"We are sending a hard message to those people who think they can come into Washington and take it over," he said. "They can forget it. We are the tough guys here."