The third tabloid newspaper company employee infected with anthrax is an administrative clerk who sometimes handled mail and express packages at the American Media Inc. building now sealed as a public health hazard and crime scene. But she inhaled so few spores of the potentially fatal bacterium that she reported for work today, feeling well.

"I just want to say I'm fine," Stephanie Dailey, 36, told reporters outside her home tonight. It was as though the wind had been knocked out of her, she said, when she learned anthrax had been discovered in her nasal passages. But she trusts the doctors who have told her that antibiotics will quickly overwhelm the bacteria.

A senior FBI official said today that traces of anthrax have been discovered in the mailroom of American Media, which publishes the National Enquirer, the Globe and several other supermarket tabloids. Two of the infected workers -- Dailey and Ernesto Blanco -- handled mail.

The only employee to contract the full-blown disease was Robert Stevens, a photo editor who died Oct. 5. Anthrax was found on the computer keyboard at his desk, two floors above the mailroom.

Authorities will not discuss publicly their theories about the source of the bacterium, which is rarely found in humans in this country -- the last fatal attack in the United States occurred in 1976. Infectious disease specialists said today that an anthrax attack could be carried out through the mail, although with difficulty.

Investigators in carefully sealed hazardous material suits have been inspecting the 66,000-square-foot building for microscopic traces of anthrax since Monday, when AMI's headquarters were evacuated and testing began for more than 1,000 people who worked or visited the site. Working in teams, the investigators have examined areas near air vents and many surfaces throughout the building. They returned to the building Monday night, after Dailey tested positive, to retrieve more samples from her work area.

FBI officials said no evidence has been found to connect the anthrax outbreak to terrorists, including the hijackers who attacked the Pentagon and New York City on Sept. 11, but the FBI has not ruled out a connection. Several of the hijackers spent time during recent months in communities near the AMI building.

Investigators are confident the anthrax is confined to the offices.

Dailey is the only employee to test positive for the bacteria, with the results of 700 nasal swab tests completed and announced publicly. Workers also gave blood samples this week. All but 10 AMI employees have reported for the tests, a Palm Beach County spokesman reported today. Seven workers are on vacation and authorities are searching for the other three.

Anthrax can be fatal, and quickly, but the bacterium is typically eradicated with antibiotics. Tim Caruso, FBI assistant director for counterterrorism, told a House subcommittee today, "There is no need for the American people to panic."

Caruso, who reported the discovery of the bacteria in the mailroom, likened the case to the recent hijacking of a Greyhound bus in which six people died, and said it "appears to be an isolated incident."

Several experts said today that the pieces of the medical puzzle made public do not point to a simple and plausible explanation for the infection of the three workers.

The fatal case of inhalation anthrax -- the rare condition that killed photo editor Stevens -- required high concentrations of anthrax spores in the air, the specialists said. If the bacteria had been blown into the offices through the ventilation system, spores should have been found on many of the work surfaces, but only the mailroom and Stevens's keyboard have tested positive.

Another possibility is that the spores arrived in a piece of mail opened by Stevens. Even a teaspoonful of spores would be far more than needed to start an infection -- if they puffed into the air and Stevens breathed them, said Martin E. Hugh-Jones, a Louisiana State University epidemiology professor.

"He wouldn't have known he had anything other than maybe some infected sinuses. He'd have a stuffy head. But then it's just a few millimeters to the brain" and the blood stream. That could lead to the full-body infection that killed Stevens, Hugh-Jones said.

But how could those spores have reached the nasal passages of the two other employees who tested positive? One theory is that they got spores on their hands -- perhaps off of Stevens's desk or computer -- then touched their noses.

Experts disagree about whether spores could fly off a keyboard and into the air in concentrations adequate to get into a keyboard user's lungs.

"The spores do tend to stick to surfaces because [of] electrostatic charges," said Jonathan B. Tucker, director of the Center for Nonproliferation Studies at the Monterey Institute of International Studies in Washington.

But Ken Alibek, who helped develop biological weapons in the former Soviet Union before defecting to the United States, believes it is possible. "You could generate some aerosol just by typing on the keyboard during the day," Alibek said.

Staff writers Eric Pianin and Rick Weiss contributed to this report from Washington.

Stephanie Dailey, 36, reported for work yesterday after being treated.