A State Department mail handler lay ill with inhalation anthrax Thursday and the besieged Postal Service set up spot checks at facilities nationwide as the bioterror scare widened.

“We still don’t know who is responsible,” said Homeland Security Director Tom Ridge.

The new anthrax case in Virginia was but one of several on Thursday:

• Postal Service says anthrax has been detected on four mail-sorting machines at a Manhattan processing station that handles millions of parcels a day.

• Health officials say a probable case of skin anthrax has been found at NBC, stemming from the same letter that is believed to have infected an assistant to news anchor Tom Brokaw.

• A second New Jersey postal worker may have the inhaled form of anthrax, health officials said. They urged hundreds of postal workers at two Trenton-area facilities to take antibiotics for 60 days instead of just seven.

Ridge said that as of midday, officials had begun environmental testing at 200 postal facilities along the Eastern corridor, presumably the region from New York to Washington.

“I want to reiterate, there is no indication of any new exposure at this time at these sites,” he said.

The infected New York postal machines are in the Morgan Processing and Distribution Center, which covers two city blocks on Ninth Avenue between 28th and 30th streets and has more than 5,000 employees.

McGovern said the building would remain open. The postal service said health officials had advised earlier that it was safe to continue working.

Louie Nikolaidis, a lawyer for the New York Metro Area Postal Union, said the building should be closed and cleaned.

“What they should do is immediately shut down the facility. They should then proceed to test all remaining equipment and the workers,” Nikolaidis said.

No postal employees have tested positive for anthrax in New York, but two have died of the inhaled form of the disease in Washington, D.C.

At least two anthrax-contaminated letters, one to NBC and one to the New York Post, passed through the city’s mail system, which handles about 20 million pieces of mail a day.

At NBC, the second case of skin anthrax has classified the case as “suspicious or probable" by the Centers for Disease Control and Prevention, the city Health Department said today.

City Health Commissioner Neal Cohen said the diagnosis was complicated because the NBC employee had been on antibiotics before a biopsy was taken, and the biopsy came up negative for anthrax.

But a blood sample, the employee’s symptoms and the fact that she had handled the Brokaw letter persuaded officials to classify the case as probable.

“The bottom line is the woman is fine,” said Kassie Canter, an NBC spokeswoman.

At a White House news conference, Ridge also disclosed that the anthrax contained in mail addressed to Senate Majority Leader Tom Daschle had been altered to make it more of a threat. “It is highly concentrated. It is pure and the spores are smaller,” he said. “Therefore they’re more dangerous because they can be more easily absorbed in a person’s respiratory system.”

Ridge said the type of anthrax used in the U.S. attacks is called Ames. Anthrax researchers have identified Ames, named for the city in Iowa, as the strain used in American bioweapons research. It also is used to test vaccines.

Three weeks into the nation’s unprecedented bioterrorism scare, lawmakers were permitted to return to several of their office buildings on Capitol Hill. And White House spokesman Ari Fleischer said there had been no evidence of anthrax exposure among officials who came in contact with mail that went through an offsite machine where anthrax was detected earlier in the week.

“We are here to conduct the nation’s business. We will not be frightened,” said Secretary of State Colin Powell as he appeared before a Senate committee.

But there were words of caution elsewhere. “We are very concerned about additional letters. We would be naive to think this is over yet,” said Dr. Julie Gerberding of the Centers for Disease Control and Prevention.

There was further jolting news, a disclosure from officials in New Jersey that a postal worker was being watched for suspected inhalation anthrax, and then the announcement from the State Department.

Dr. Ivan Walks, head of the Washington public health department, said the man was hospitalized in guarded condition with inhalation anthrax. Unlike other area residents who have been hit, this patient had been asked whether his job required him to go to the Brentwood postal facility that serves as the main mail processing center for the nation’s capital.

“His answer was ’never,”’ Walks reported.

However, mail to federal agencies passes through the contaminated Brentwood facility.

That announcement came in addition to 12 confirmed cases of anthrax in the past three weeks, most of them linked to anthrax-spiked mail that has passed through New Jersey, New York or the nation’s capital.

One such letter was addressed to Daschle; others are known to have been sent to NBC News anchorman Tom Brokaw and to the New York Post. Anthrax has also been found in Florida, where one man died, although authorities have not yet found tainted mail there.

At his White House news conference, Ridge said tests on the anthrax found to date confirmed it is all of the same strain and responds to antibiotics, meaning that “people who are exposed can be treated.”

At the same time, he added, the substance in Daschle’s mail “has some different characteristics” that make it more easily taken into a victim’s lungs. He said that based on the latest lab reports, “It is clear that the terrorists responsible for these attacks intended to use this anthrax as a weapon.”

In all, 28 people were exposed to anthrax in and around Daschle’s office, and all Senate office buildings were shut down. The discovery of anthrax on a mail machine in a House office building prompted the closure of additional office buildings.

Daschle said one wing in the building that houses his office would remain sealed off for the indefinite future. “I am very confident that we will be able to seal it in a way that will provide us complete confidence that we can access the rest of the building without any hazardous exposure,” he told reporters in the Capitol.

Officials learned Wednesday of additional anthrax in the same building when tests taken from a freight elevator turned out positive. Congressional sources, speaking on condition of anonymity, said the elevator is used routinely to convey express mail to the Hart Building, connected by underground tunnel to the Senate’s main mail room in the building next door.