U.S. military strikes on Afghanistan in response to the Sept. 11 attacks on the World Trade Center in New York and the Pentagon near Washington have put jittery officials and citizens nationwide on the alert for possible new attacks.

Lisa Farbstein, a spokeswoman for the Washington Metropolitan Area Transit Authority said Judiciary Square and Gallery Place-Chinatown metro stations were closed at the request of the local fire department after the Judiciary Square station manager reported a suspicious smell.

Firemen turned a Reuters reporter and other passengers away from the Union Station subway station at one point also, but metro and fire department officials said it was not closed.

Farbstein and fire department spokesman Alan Etter said the smell was similar to that of natural gas, although a hazardous materials squad later found no gas in the subway tunnel.

"There was an odor but there was no instrumental detection of any gas," said Etter.

He said a gas smell had been reported this week evening at the MCI Center sports complex near the Gallery Place metro station and that Washington Gas was investigating whether a nearby construction site might be the source of any gas leak.

"We live in very unique times since Sept. 11 and whenever something unusual happens we are leaning toward caution," metro's Farbstein said. "As you can see from the past couple of days, we take everything very seriously and we are continuing to run a safe transit system."

In Florida, FBI investigators in protective gear yesterday searched for the source of the anthrax that killed a Florida man, as state health officials said they had not dismissed any explanation for the incident.