WASHINGTON - As sirens blared and clouds of gray smoke wafted across town from the Pentagon - signaling that the nation's capital, like New York, had been attacked by terrorists - hundreds of thousands of people poured out of downtown yesterday in an eerie midmorning exodus.

With all federal buildings evacuated and most other businesses, museums and restaurants shut down, scores of employees and tourists jammed onto the sidewalks and parks, some shaken, some tearful, some in disbelief.

"I think we're at war," said Neil Hare, a lawyer for the U.S. Chamber of Commerce who works near the White House. He planned to walk to his parents' house in Rockville rather than to his own home near the State Department. "I'm running. This is probably ground zero, and I don't want to be anywhere near here."

Hare, who quit smoking four months ago, stopped to buy a pack of Marlboro Lights for his long trek to Maryland in his business suit and dress shoes.

"Nicorette gum isn't going to do it for me today," he said.

Many struggled to remain calm and figure out how to get home and contact family members.

"I can't reach him," wailed one woman whose husband works at the Pentagon, which suffered a devastating blow from a hijacked plane. "I called over there, and all I could hear was chaos in the background."

By midmorning, several streets, including those near the White House, and parts of the subway system had been closed, and traffic clogged the streets.

Firetrucks and ambulances tried to snake through, their sirens joining with honking horns and the roar of rescue helicopters and F-16 fighter jets patrolling the blue skies above Washington to create a scene that many said seemed unreal, like Orson Welles' 1938 broadcast of War of the Worlds.

"I hope I'm still asleep," said Darryl Day, a banker.

Adding to the sense of unease, police carrying submachine guns patrolled in front of the White House, and bomb-sniffing dogs were stationed near the World Bank and other federal buildings.

Police combed through trash bins in the subway stations. All day, they stood guard with shotguns along a four-block perimeter around the White House.

Lines at pay phones

For many, cell phones proved useless, and lines formed at pay phones.

"This is starting to be quite frightening," said Phil Hall, a forester from Oregon on assignment to the Interior Department. Hall had been staying at a hotel near the Pentagon and did not know where to go.

"We have a lot of security that's more narrowly focused - electronic keys for every door, even a password to get into the restroom - but something of this scale is hard to grasp," he said. "Now, all of a sudden, you don't know where to go, you don't know where to hide."

Hall said he tried to call his wife at home before he evacuated the Interior building, but the phone lines were dead. "I really wish I could have talked to her before I left," he said.

Many wondered how an attack of such magnitude could have caught the United States by surprise. Others said they felt it was inevitable in a dangerous world.

"This has been a long time coming," said Candace French, an Annapolis resident who was flagging down any car with a Maryland tag for a ride back home. "We have had our eyes opened now."