for hours, generating thick clouds of smoke that streamed and billowed in a brisk wind.

The blaze broke out on the Army post in Anne Arundel County and 3:05 p.m. and continued to burn well after 10 p.m. The fire damaged upper portions of the sprawling three-story building, which is headquarters to the 902nd Military Intelligence Group and houses several contractors, officials said.

The cause of the blaze, which apparently began on the peaked roof of the red-brick building, was not immediately known and was under investigation.

"Everyone in the building was evacuated safely, and we had one firefighter who sustained a minor injury to his leg," said Jennifer Downing, a Meade spokeswoman.

Downing declined to discuss the building's contents, calling them "sensitive in nature."

Another official said most of the documents in the damaged section are locked in fire-resistant containers and backed up elsewhere. Nothing lost at the building would adversely affect national security, said Donald Shiles, director of the Technical Counterintelligence School at Fort Meade.

A worker outside the building spotted the fire when it was relatively small, but the blaze quickly spread, said Army Lt. Col. James Peterson, director of emergency services for the post.

As darkness fell, motorists on the Baltimore-Washington Parkway called U.S. Park Police to ask about the glow created in the sky by the flames. Park Police said no roads were reported closed, and rush-hour traffic was not affected.

At one point, flames appeared to leap from everywhere on the roof of a section near one end of the multi-wing building. Flaming portions of the roof were visible amid streams of water and clouds of black and gray smoke.

Peterson said the fire was largely contained to the building's attic, which is used as office space by the intelligence group. A portion of the roof collapsed, and parts of it were "a total loss," Peterson said.

The building remained intact. "The structure did not collapse, and there does not seem to be any danger of it," said Rich Lane, a spokesman for the post. Lane said that no estimates of damage were available but that he expected it would be significant structurally and monetarily.

The cause of the fire was being sought by the Army's Criminal Investigation Division, but officials said this was routine and did not mean criminal intent was suspected.

Peterson noted that "there was minor construction going on in the area" but he made no connection between the construction and the blaze.

The barrackslike building, which is near a movie theater and chapel, dates to the World War II era, Lane said.

Anne Arundel firefighters, called immediately to help the post fire department, sent the amount of equipment and personnel that would be used to battle a four-alarm fire.

"We originally sent three engines and a truck, and it escalated from that," said Lt. Russ Davies, a spokesman for the Anne Arundel Fire Department. Before the blaze was under control, firefighters from Prince George's and Howard counties joined in the effort.

Firefighters in a ladder truck directed streams of water onto the blaze, which could be seen on an Army video.

Fort Meade is home to more than 30,000 workers.

The fire did not affect the National Security Agency, whose headquarters is also at the post.

As described on its Web site, the 902nd group conducts counterintelligence activities in support of Army commanders and protects Army forces, secrets and technology by detecting, identifying, neutralizing and exploiting foreign intelligence services and international terrorist threats

A number of military intelligence units are based at the post.

Staff writers Walter Pincus, Sandhya Somashekhar and Martin Weil contributed to this report.