Federal agents raided outlaw motorcycle gangs across the country yesterday, arresting 53 gang members in 18 states and seizing machine guns, silencers, bombs and drugs, officials said.

The operation, run by the Treasury Department's Bureau of Alcohol, Tobacco and Firearms, included the seizure of a California drug laboratory used for producing methamphetamine.

Federal agents, accompanied by state and local police, arrested leaders of the Hell's Angels, the Outlaws and the Bandidos, three of the top four outlaw gangs. Fifteen of the arrests were made earlier, officials said, and about 100 are expected by the time the first phase of the operation is completed today.

The 12-month investigation is known as "Operation One Percenter," taken from the statement by mainstream motorcycle clubs that outlaws make up about 1 percent of American motorcyclists.

Special agent Mike Catlett, who supervised the operation from the bureau's command center here, said that agents seized 10 machine guns, six silencers, parts for 20 silencers, 10 sawed-off shotguns, four hand grenades, one dynamite bomb, five pounds of dynamite, 100 handguns and 15 stolen vehicles.

Most of the silencers were seized at a Hell's Angels chapter in Los Angeles. Large amounts of drugs -- including cocaine, marijuana and pentachlorophenal, or PCP -- were seized in the raids, officials said.