An employee at the National Institutes of Health was arrested yesterday, accused of making an anthrax threat against an assessor's office in Florida with which she was having a property tax dispute, the FBI's Miami office said.

Michelle Ledgister, 43, of Bethesda surrendered to federal agents on the parking lot of a Rockville strip mall near her work at the National Institute of Allergy and Infectious Diseases, said Special Agent Judy Orihuela, an FBI spokeswoman.

After losing a claim for property tax relief on a home she owned in Parkland, Fla., Ledgister late last month left a voice mail message at the Broward County Property Appraiser's Office in Fort Lauderdale, her arrest warrant said.

In the message, Ledgister identified herself, mentioned she worked for NIH and said, "You guys now have Anthrax spores once again, so do be careful," according to her arrest warrant.

"I guess she stewed over it and got angry," said Cazi Navarro, an investigator in the assessor's office who investigated and then rejected Ledgister's tax claim.

Navarro said Ledgister sought a property tax exemption given to Florida residents, but she did not qualify because she rented out the house and lived in Maryland.

He said he had exchanged several e-mails and had telephone conversations with Ledgister - from her workplace at the NIH - and she had been calm and agreeable.

No anthrax found

A hazardous-materials team from the Broward County Sheriff's Office searched the county government building housing the assessor's office, but found no evidence of anthrax, according to the arrest warrant.

Ledgister is a quality control and assurance officer at the NIH's allergy and infectious diseases division in Bethesda, said John Burklow, a spokesman. He said Ledgister did not have access to anthrax, and the laboratories use a harmless form in their research. He said NIH was cooperating with the investigation.

Her attorney, Assistant Public Defender Daniel W. Stiller, said Ledgister's initial court appearance in U.S. District Court in Greenbelt yesterday was a "humiliating experience" for her. "She certainly recognizes the gravity of the charge against her."

She has been charged with knowingly conveying false information and hoaxes, a charge under the 1994 federal terrorism prevention act, according to her arrest warrant.

Scientists at the National Institute of Allergy and Infectious Diseases research anthrax and other potentially deadly bioterror threats, according to the institute's Web site. They are studying the effects of anthrax to develop better diagnoses and improve vaccines.

The toxin is considered among the country's most dangerous bioterror threats. In October 2001, five people, including a man in Boca Raton, Fla., died after inhaling anthrax spores that were sent through the mail.

Ledgister has owned the one-story brick house in an "exclusive neighborhood" since 1994, Navarro said. The house's value was assessed at $183,000, he said. She enjoyed tax relief for a year, but after an investigation, she was ordered to pay back the relief plus interest - about $2,300.

Voice mail message

According to the arrest warrant, Ledgister's voice mail message said: "It's Michelle Ledgister. I must commend your skillful sleuths in knowing where the main campus of NIH is located. But what they didn't tell you is that NIH is located where infectious agents are, and you guys now have Anthrax spores once again, so do be careful. Toodles."

Magistrate Judge William Connelly ordered Ledgister held in federal custody until her extradition hearing, scheduled for 2:30 this afternoon, according to federal prosecutors. Lawyers expect the case to be moved to the Southern District Court of Florida.

Sun staff writer Matt Dolan contributed to this article.