Authorities arrested two men yesterday and were seeking a third on charges that they belonged to a gang of heavily armed robbers that struck six banks in as many months in the Washington area.

Law enforcement officials, in announcing federal charges yesterday against nine alleged members of the gang, presented new details about the operation. They said the men planned each robbery methodically and obtained masks, body armor and a cache of assault rifles to intimidate clerks and patrons. More than $361,000 was stolen in the holdups, authorities said.

"These men struck bank after bank in broad daylight and with cool precision, terrorizing bank employees and patrons," U.S. Attorney Kenneth L. Wainstein said. "They operated that robbery ring with an impressive level of planning, preparation and operational discipline."

Eight of the nine suspects are in custody on charges of bank robbery, conspiring to commit bank robbery, weapons violations and racketeering. Members of the gang allegedly fired shots during several of the robberies, including once at a police officer.

Police arrested one man, Bryan Burwell, 27, yesterday morning in Lanham. A second, Carlos Aguiar, 24, was arrested yesterday afternoon after a brief car chase in Southeast Washington. U.S. marshals fired at Aguiar during the chase, but no one was injured, authorities said.

Omar Anderson, 23, who is being held on unrelated charges in another state, was served yesterday with a warrant charging him in the robberies, authorities said.

Authorities were seeking a ninth man, Omar Holmes, 26, of the 900 block of Euclid Street NW. Other arrests are possible, they said.

Five other men were arrested last month. One of them, Nourredine Chtaini, 29, pleaded guilty Monday to racketeering. Chtaini cooperated with authorities, helping investigators conduct raids that broke up the group July 16, law enforcement officials said.

According to an indictment, a charging document and Chtaini's plea agreement, which were unsealed yesterday, Chtaini and Miguel Morrow, 26, of the 700 block of Marietta Place NW, participated in the six robberies.

On Jan. 21, Chtaini, Morrow, Anderson and Aguiar decided to commit a series of robberies, beginning with a holdup of an armored car, according to Chtaini's plea agreement.

The group waited for several hours at Wisconsin Avenue and Emory Street NW but eventually gave up, according to court records, and decided to hit a bank the next day.

That next morning, Morrow, Chtaini, Anderson and Holmes entered the Bank of America branch in the 5900 block of Blair Road, carrying assault rifles, according to Chtaini's plea agreement. Chtaini took a .38-caliber revolver from a pregnant guard, according to court records, and the men fled with more than $144,000, the plea agreement shows.

On March 5, the four men allegedly stole more than $92,000 from a Riggs Bank on Georgia Avenue NW.

Two months later, the gang robbed a Chevy Chase Bank in the 3600 block of St. Barnabas Road in Temple Hills, the records allege. Morrow, Aguiar and Chtaini went inside the bank while a fourth man -- identified as Lionel Stoddard, 21, of the 700 block of Marietta Place NW -- remained outside as a lookout, authorities said.

Stoddard fired an assault rifle at a responding Prince George's County police officer, authorities said.

The other men jumped into a getaway van and fired out of the back of the vehicle to distract police officers in pursuit, according to the court records.

The gang carried out three more robberies with the same precision, authorities said.

The final robbery, of a SunTrust branch in the 5000 block of Connecticut Avenue NW, was captured on videotape by a television cameraman who was working on another story.

Prosecutors and police declined to comment on where the robbers spent their money or how they came together as a gang. But Wainstein said the robbers hit a Chevy Chase Bank in Prince George's on May 27, netting about $18,000, to help finance a Memorial Day trip to Florida.

Aaron B. Perkins, 27, and Guidel Olivares, 45, also are charged in the conspiracy. The two men were arrested last month in raids.

Federal officials yesterday said D.C. police and federal agents conducted surveillance on Chtaini because they suspected his involvement in two shootings this spring in Northwest Washington.

On July 11, Chtaini, having spotted a police helicopter, drove his car to Alexandria, where he crashed and then attempted a carjacking at gunpoint before he was arrested. He later admitted his involvement in the bank robberies to investigators, who were led to him after receiving tips, authorities said.

The robbers struck "with cool precision," U.S. Attorney Kenneth Wainstein says.