Federal law enforcement officials said yesterday they have arrested more than 100 members of Jamaican gangs in a crackdown on a segment of the crime world they consider "one of the country's most violent."

Stephen E. Higgins, head of the federal Bureau of Alcohol, Tobacco and Firearms, said at a news conference that 118 gang members have been arrested since Monday in a sweep in the District of Columbia and 13 states. Higgins said he expects more than 200 arrests this week in the first stages of the crackdown.

Higgins said the investigations, by multiagency Organized Crime and Drug Enforcement Task Forces across the country, have identified 20 Jamaican "posses," a term the groups gave themselves, taking the name from television westerns.

He said the groups have been connected to more than 600 drug-related homicides, as well as narcotics trafficking, kidnapings, firearms offenses, robberies, assaults and money laundering. The gangs started in marijuana trafficking, but are now extremely active in the cocaine trade, operating a number of "crack" houses in U.S. cities, Higgins said. He said those arrested are mostly illegal aliens.

Higgins said those in custody would be charged with federal immigration and firearms offenses as well as a variety of state criminal charges.

Agents seized narcotics, cash and a number of firearms, including automatic weapons, in arrests here and in New York, Miami, Baltimore, Boston, Philadelphia, Cleveland, Dallas, Denver, Houston, Kansas City, Chicago, Atlanta, Detroit and Los Angeles, according to Higgins. A total of 13 Jamaicans were being sought in the Washington and Baltimore areas.

The posses began to set up operations in the United States in the early 1980s and are believed to number several thousand members, most of them in their early 20s to early 30s, Higgins said. The highest concentrations of the Jamaican gangs are in the New York City area, in southern Florida and around Kansas City, he said, but the gangs are now considered a national phenomenon.

Dallas, one of the first cities in which the sweep got under way, accounted for about one-third of the arrests. Police there said they had arrested 45 Jamaicans believed to have been involved in drug wars between rival Jamaican gangs that have resulted in 44 murders.