"The good news is that everyone will be OK," the South Dakota Democrat said, noting all had been on antibiotics since shortly after the potentially deadly anthrax bacteria was found in a letter opened in his office on Monday.

Daschle was not in the office at the time.

But leaders of the Republican-controlled U.S. House of Representatives decided to close at the end of business yesterday for anthrax testing on their side of the building. It marked an unprecedented halt to business for an environmental safety check. Daschle said the Senate would remain at work while three Senate office buildings were closed for expanded safety checks.

"I am absolutely determined to ensure that the Senate continues to do its work," said Daschle.

"There is no risk here at the Capitol," said Senate Minority Leader Trent Lott, a Mississippi Republican, who joined Daschle at a news conference.

For a third straight day, congressional staffers stood in line for anthrax tests.

Daschle announced the extent of the exposure two days after the nationwide anthrax scare in the wake of the Sept. 11 attacks on the United States reached the Capitol.

The anthrax letter opened in Daschle's office was similar to one sent to NBC anchor Tom Brokaw in New York. Both were postmarked Trenton, New Jersey. A third letter was sent to a tabloid newspaper in Florida, where anthrax spores killed a photo editor and sickened a mail room worker.

U.S. officials have said they suspect but have no firm evidence the anthrax scare could be linked to Saudi-born Osama bin Laden, accused of masterminding the attacks that killed nearly 5,400 people in New York, Washington and Pennsylvania.

The reaction in the nation's capital reflected the jumpiness around the country. Baltimore police went on high alert after reports of a possible anthrax attack but found nothing.

Tests were also ordered in the Manhattan office of New York Gov. George Pataki but he said neither he nor his staff tested positive. Preliminary tests on powder sent to an abortion clinic in Stuart, Florida, showed anthrax but officials called it "extremely unreliable" and speculated it was talcum powder.

Health and Human Services Secretary Tommy Thompson tried to calm fears by announcing a significantly expanded $1.5 billion federal drive to stockpile drugs and vaccines to counter not only anthrax but other potential agents of germ warfare such as smallpox.

Daschle said 31 congressional employees had tested positive for anthrax exposure, including about 25 of his own staffers, plus a number of Capitol police officers who came to his office when the letter was opened.

Sen. Russ Feingold, a Wisconsin Democrat, said three of his employees had tested positive for anthrax exposure. They worked in Feingold's office, which is next door to Daschle's office in the Senate Hart Office Building.

It was not immediately clear if the three Feingold staffers were among the 31 reported by Daschle, or in addition to them.

Daschle said, however, the Senate Hart Office Building and two others would be closed for further testing. He said there was no indication that anthrax had spread, but authorities wanted to make sure.

Authorities said the type of anthrax found in a letter was not as potent as first suspected, but it had been processed and was potentially lethal.

Maj. John Parker from Fort Detrick, Maryland, an Army facility that confirmed the powdery substance was anthrax, said, "It's common variety from all our testing at this point."

He also characterized the sample as "pure spores" but said it appeared to be sensitive to all the major antibiotics used against anthrax, a sign it had not been genetically manipulated to be even more dangerous.