Flak-jacketed FBI agents broke through the door of a Southeast Washington home late Tuesday night and arrested the alleged ringleader of an area bank robbery gang after he attempted to escape by jumping from a third-floor window.

Agents captured Nathan Orrin Joseph, 23, at gunpoint after he landed on the ground and dashed out of the back yard of the home in the 1300 block of Valley Place. More than a dozen agents participated in the capture.

Joseph, the object of a months-long FBI manhunt, was charged with armed robbery of two banks in suburban Washington -- the Lincoln National Bank in Gaithersburg last May and Equitable Trust Co. in Camp Springs in September. Agents said Joseph masterminded both holdups and is a suspect in several others carried out by a District-based gang. The group, believed to consist of at least four men, has made off with more than $100,000 from bank robberies in the last six months, according to sources familiar with the investigation.

FBI officials said the Gaithersburg and Camp Springs holdups were unusually violent. A witness was shot and seriously wounded each time, and other customers and bank employes were roughed up, officials said.

"It's like Dodge City -- lots of guns and violence," said one law enforcement official.

When agents arrested Joseph Tuesday, they said they found a loaded .38-caliber revolver and bullet-proof vest in the Valley Place house. In July, FBI agents said they found a shotgun, a rifle and a pistol as well as an unspecified amount of heroin when agents searched another District residence where Joseph allegedly was living at the time. Joseph was not in the house during the July raid and remained at large until Tuesday, agents said.

Yesterday, Joseph, dressed in jeans and a sweater, limped into U.S. District Court where he was arraigned before U.S. Magistrate Jean F. Dwyer. His lawyer, Kenneth Michael Robinson, told the magistrate Joseph may have broken his leg when he jumped out the window Tuesday night. Dwyer ordered Joseph held under $50,000 bond and recommended he receive medical treatment for his injury.

Joseph was indicted June 24 by a federal grand jury in Baltimore in the Gaithersburg bank robbery. In that case, the FBI said, four armed and masked men entered the bank May 30 and announced their arrival by firing a shot into the bank's ceiling. When a bank customer attempted to tackle one of the armed suspects, the bandit shot and wounded the customer, agents said.

In the Camp Springs holdup on Sept. 17, a gang member fired on and wounded another witness as the gang fled in a getaway car, according to the FBI. The shooting occurred after the suspects spotted the witness writing down the getaway car's license tag number, the FBI said.

Three other suspects in the robberies are still at large and are being sought by the FBI.