WASHINGTON?A sample taken from a plastic evidence bag containing a still-unopened letter to Sen. Patrick Leahy contains at least 23,000 anthrax spores, enough for more than two lethal doses, a federal law enforcement official said Tuesday.

The official, speaking on condition of anonymity, said there were three times more anthrax spores in the single sample taken from the plastic bag than in any of the other 600 bags of mail examined by the FBI before it found the Leahy letter.

Meanwhile, traces of the bacteria have been found in the office mailrooms of Sens. Edward Kennedy, D-Mass., and Christopher Dodd, D-Conn. Both senators issued statements expressing concern for their staffs, but said they’ve been assured that there is no health risk.

Officials suspect the anthrax got there through contact with anthrax-bearing letters mailed to Leahy or Senate Majority Leader Tom Daschle, D-S.D.