The third man to be diagnosed with inhalation anthrax, a D.C. postal worker, was said Sunday to be "gravely ill" by Mayor Anthony Williams.

Doctors confirmed Sunday that the unidentified man had the most serious form of the disease after he checked into a Fairfax, Va., hospital Friday with flu-like symptoms.

More than 2,000 employees at the central mail-processing center for the nation's capital and another 150 employees at the air-mail handling center near Baltimore-Washington International Airport would be tested for exposure to anthrax spores beginning Sunday afternoon, said Williams.

In all, more than 6,000 workers on Capitol Hill — including postal employees, congressional staffers and maintenance employees, police officers and visitors — have been tested since a letter containing anthrax was discovered Monday in Senate Majority Leader Tom Daschle's office.

Unlike its skin-contracted counterpart, anthrax inhaled through the lungs is usually fatal. One man in Florida died from it earlier this month, and a second man was in critical condition but has since been steadily recovering. 

Earlier Sunday, D.C.'s chief health officer said the third man was taking antibiotics and expected to make a full recovery.

"Right now he's clinically stable and being treated," said Dr. Ivan Walks. 

The patient works in Washington's central mail handling facility, which processed an anthrax-tainted letter sent to Daschle. It was not known whether the worker was exposed to the bacteria from that letter. 

The disease has spread through tainted letters in the six weeks since the Sept. 11 terrorist attacks in Washington and New York. 

In all, nine people have been diagnosed with anthrax, six of them with the less serious skin form. 

Dan Mahalko, a U.S. Postal Inspection Service official in Washington, said the Centers for Disease Control and Prevention began testing employees at the Brentwood facility's government mail section for possible anthrax exposure a few days ago. 

He said the CDC also ran tests on the mail machinery. 

Meanwhile, New York City Mayor Rudoph Giuliani said Sunday that a host of tests performed at media organizations in the city had come back negative for evidence of anthrax. 

He said environmental tests at ABC, where the 7-month-old infant son of a producer was believed to have contracted the disease, had also returned negative. He investigators had not identified the source of the child's infection, and no suspect letter had been found. 

Giuliani said Sunday that the number of New Yorkers infected with the bacterium remained at four, with one case each at NBC, CBS, ABC and the New York Post. "There are no others," he said. 

The news of the third case of inhalation anthrax in D.C. came after more traces of the bacteria were found in the federal government complex, this time in a House of Representatives office building only a few blocks away from the Capitol. 

Health inspectors found the toxic bacteria in a machine used to process mail for lawmakers, widening the reach of the anthrax threat and marking the first time traces have been found on the House side of Capitol Hill. 

Rep. Charles Bass, R-N.H., said all other machines tested negative, as did the House child care center. The swab of the infected machine was taken Wednesday. Positive test results for anthrax were confirmed Saturday. 

The discovery was "not an unexpected situation," according to a spokesman for the U.S. Capitol Police. 

"It is exactly why we have been performing sampling throughout the Capitol complex," said Lt. Dan Nichols. 

Nasal swabs will be used to test workers in the building's mailroom for exposure to anthrax, according to Nichols. But he said federal health officials are not recommending screening for other employees. 

The latest developments capped a week that thrust Congress in the center of the anthrax-by-letter scare and more than doubled the number of Americans infected. 

President Bush vowed to fight the "act of terror" that has killed one person, sickened seven others, forced thousands to undergo preventive treatment and frightened millions more. 

Speaking from China, where he was attending an international trade meeting, the president said there was no evidence the anthrax letters were linked to the Sept. 11 attacks. 

Investigators focused their work on Trenton, N.J., where the letters to Daschle and NBC Nightly News anchorman Tom Brokaw were mailed. More than 150 FBI agents and postal inspectors were on the scene. 

A letter mailed to the New York Post, also postmarked Trenton, has tested positive for anthrax and is similar to anthrax-laced letters sent to Brokaw and Daschle, law enforcers said. 

The letter addressed to the "Editor" at the Post was postmarked Sept. 18 — the same day as a contaminated letter sent to Brokaw. The letter to Daschle was postmarked Oct. 9. 

Investigators have concentrated on Trenton since a letter carrier there contracted skin anthrax. They are combing houses, apartments and the few businesses along her route for clues. 

At least 200 other postal employees who work in the same buildings as the three in New Jersey who have tested positive were given a seven-day supply of the antibiotic Cipro. 

The discovery of the deadly bacteria in the House's Ford Office Building has rattled Capitol Hill. Anthrax had already been discovered in two Senate office buildings — in a mail facility in the Dirksen building and in Daschle's office in the Hart building. 

Thirty-one people tested positive for exposure to anthrax earlier this week after powdery substance fell from mail opened in Daschle's office. They included 23 aides to the majority leader, five police officers and three people on the staff of Sen. Russ Feingold, D-Wis., who occupies the office next to Daschle's. 

Police declared two Senate office buildings off-limits to check the spread of spores on Capitol Hill. 

"No member, staff member or congressional employee will be permitted to enter" the Dirksen or Hart Senate office buildings without personal protection gear," said a memo issued by officials. 

One congressional source, speaking on condition of anonymity, said another 1,300 people at the Capitol showed no sign of exposure in tests completed overnight. Hundreds more awaited their results. 

The threat and scare of bio-terror morphed into a global affair. From Australia to the Netherlands, from Spain to Brazil, authorities fielded hundreds of reports of tainted letters and suspicious powders. While most of the reports have been quickly dismissed as hoaxes — pranksters have been detained in Australia, the Netherlands and Spain — other scares proved authentic. 

On Friday, Argentine Health Minister announced that a travel brochure mailed from Florida to a house in Buenos Aires tested positive for anthrax spores. The recipient of the letter was not infected. 

Earlier this week in Kenya, a doctor received an anthrax-tainted letter from Atlanta. The doctor and his family were in good health but were being treated with antibiotics. 

Police reported Saturday that a powder-laden letter sent to the U.S. consulate in the western Japanese city of Osaka was determined to be untainted. 

A Brazilian laboratory said Saturday that material contained in a letter sent to the Rio de Janeiro bureau of The New York Times had tested negative for anthrax. 

Federal investigators confirmed Friday that the strains of deadly anthrax spores mailed to New York, Washington and Florida are virtually identical. In Washington, Homeland Security Director Tom Ridge also said anthrax strains discovered in Florida, New York and Washington are indistinguishable from one another, and have not been "weaponized." 

"It does appear that it may have come from the same batch," Ridge said at a White House news conference. He added, "It may have been distributed to different individuals to infect and descend into different communities." 

He said that so far there are no test results to suggest the anthrax had been weaponized, meaning altered to make it spread more easily in the air. 

One man has died and a second man remains ill in Florida after inhaling anthrax spores. The other reported cases of anthrax have involved cutaneous or "skin" anthrax, a less serious form. 

Investigators and administration officials said they still had no evidence to connect the bioterrorism to the Sept. 11 suicide hijackings that killed more than 5,000 people. 

"I do not have knowledge of a direct link of the anthrax incidents to the enemy, but I wouldn't put it past them," President Bush said at a news conference in China. 

Attorney General John Ashcroft raised the possibility that the anthrax attacks could be the work of more than one homegrown terrorist, but said he couldn't rule out a connection between the anthrax attacks and the events of Sept. 11. 

One scenario being explored is whether someone living in the United States might have worked with a foreign country or an overseas domestic terrorist group with enhanced biochemical capabilities, officials said. 

"It might well be that we have opportunists in the United States or terrorists in the United States who are acting in ways that are unrelated," the attorney general added. 

Ridge said the administration was preparing for the threat of additional anthrax attacks. 

"I wish I could tell you that we have seen the end of it, but obviously we are preparing for more. That's why we have increased the supply of antibiotics," he said. 

The Associated Press contributed to this report.