D.C. Boosts Security For Holiday Festivities

"The best way to deal with [the threat] is to go on offense and have unpredictable security measures," Hawley said in a telephone interview from Paris, where he was meeting with his European counterparts.

Law enforcement officials said residents shouldn't be so unnerved that they stay away from the Mall festivities.

"This is probably the biggest and best-coordinated effort I've seen" for a major public event in the D.C. area, said Christopher Geldart, who heads the National Capital Region office at the Department of Homeland Security.

But the U.K. incidents have left some Americans wary.

Fort Belvoir barred the public from its July 4 fireworks display and moved it from the north side of Route 1 to Pullen Field on the southern part of the post. The decision was "a precautionary measure following events in the United Kingdom," the announcement said.

Arlington Fire Chief James Schwartz said law enforcement officials are concerned that seemingly amateurish plots such as the ones in Britain could be a way to "test our response, be a surveillance of our response efforts."

Is he worried about trouble on the Fourth of July?

"We're worried every day we come to work," he said. "We always try to remain vigilant."

Staff writers Bill Brubaker, Daniela Deane, Maria Glod and Eric M. Weiss and staff researcher Julie Tate contributed to this report.