WASHINGTON?Thirty-one Senate employees tested positive for anthrax exposure, officials said Wednesday as the threat of bioterrorism rattled Capitol Hill. Hundreds more lined up nervously to be tested, and leaders ordered the shutdown of the House and three Senate office buildings.

?We?re in a battle with terrorism, a new form of human warfare,? said House Democratic leader Dick Gephardt. Officials confirmed evidence of exposure in a second Senate office?adjacent to Majority Leader Tom Daschle?s suite where an anthrax-spiked letter was opened earlier this week?as well as spores in a centralized mail room in a building across the street.

The Senate announced plans to close all three of its sprawling office buildings, but in a gesture of defiance aimed at terrorists, made plans to convene Thursday.