The letter that infected Brokaw's assistant with the skin form of anthrax was addressed by hand and the envelope had unspecified "distinguishing characteristics," a state source familiar with the FBI investigation said on condition of anonymity.

The letter was postmarked from Trenton on Sept. 18, the same day another anthrax-contaminated letter from Trenton was sent to the Washington office of Senate Majority Leader Tom Daschle.

The Daschle letter bore the return address of a nonexistent New Jersey elementary school. The Justice Department released copies of the envelope with a handwritten return address for the fourth-grade class at the "Greendale School" in Franklin Park, N.J.

The street address appeared to be fictional and is outside the region covered by the Trenton Post Office. The contaminated letter to Brokaw had similar block printing but no return address.

The second Brokaw letter, postmarked Sept. 20 from St. Petersburg, Fla., contained a powdery substance but tested negative for anthrax.

The third letter was mailed Sept. 18 by a Statehouse secretary who found it inside a Federal Express package sent to the governor's office.

The envelope she mailed had a typewritten address and did not look like the contaminated letter, two state government sources said. They said the secretary threw out the original Federal Express envelope.

State police are trying to determine through Federal Express records where the package came from. It was unclear what happened to the letter.

Meanwhile, state health spokeswoman Marilyn Riley said two Trenton postal employees who may have handled tainted letters are not infected with anthrax.

Across the state this week, there have been more than 350 reports of suspicious packages, powdery substances and other items feared to be biological terror weapons.

Four state office buildings were evacuated Tuesday morning, straining police resources and angering acting Gov. Donald T. DiFrancesco. He warned that hoaxes would not be tolerated.

"It's nothing short of treason at a time of war," DiFrancesco said.

Between Sept. 11 and Saturday, state emergency management officials logged 68 reports of suspicious materials, State Police spokesman John Hagerty said. By Tuesday, that number had grown to 425.