Authorities evacuated the Washington Monument and shut down traffic on nearby streets yesterday afternoon after police received a bomb threat that turned out to be a hoax.

Police said a man called the District's 911 center about 2:30 p.m. and threatened to blow up the monument. U.S. Park Police quickly evacuated tourists and employees from the historic structure and then shut down surrounding roads, including Independence and Constitution avenues and 15th and 17th streets NW.

Bomb-sniffing dogs combed the building and grounds but discovered no explosives. Police reopened the monument and surrounding area at 4:15 p.m. The road closures, coupled with a heavy rain, caused widespread gridlock.

U.S. Park Police Chief Dwight E. Pettiford said authorities felt they could not take a chance in dismissing the threat.

"In today's times, we have to take all threats seriously. . . . You can't cut any corners," Pettiford said. "We want to assure the public that we are doing the right things."

Pettiford said police were monitoring the situation in New York, where security has been stepped up on subway trains and in terminals since Thursday. New York Mayor Michael R. Bloomberg said that the city had received a "specific threat" against the transit system.

No one was arrested for the monument scare. Other officials said investigators were looking into the possibility that the threatening call came from someone using a pay phone at the Tenleytown-AU Metro station. Metro officials said that transit police planned to view surveillance tapes.

Sgt. Scott Fear, a Park Police spokesman, declined to say how frequently threats are made against the monument.

For two hours yesterday during a major rain shower, groups of tourists were turned away from the monument grounds with shrill whistles and stern warnings from police officers encircling the obelisk. In a typical day, about 1,700 visitors ride an elevator to the top of the 555-foot monument.

Police first closed off 15th Street and Constitution and Independence avenues and then widened the perimeter about an hour after the threat. Pedestrians sloshed through puddles and frantically maneuvered strollers across the Mall.

Tourists said they understood why police were being so careful.

"This is not the Washington I knew," said John Evler, who grew up in suburban Maryland and now lives in Austin. "When I was here, it was for peace marches and protests in the '60s," he said, shaking his head. "Bomb scares: That's new. Scary world. Scary."

Dave Hunt was waiting in line to get his ticket to tour the Washington Monument when Park Service personnel turned him away. Then police officers hustled past him with bomb-sniffing dogs.

"I walked up to the top of the monument 45 years ago. Thought I could get up there again today," said Hunt, who was visiting from Kentucky and was determined to wait out the bomb threat. "I'll get back in there once it's back open. I'm not going to change my lifestyle because of what some idiot did."

Staff writer Karlyn Barker contributed to this report.

The Washington Monument was closed because, as a police official said, "we have to take all threats seriously."