WASHINGTON, April 28 — Deborah Jeane Palfrey has not been at all shy about it: for more than a decade she ran an escort service that catered to upscale clients in the nation’s capital, sending college-educated women to men’s homes or hotel rooms.

For about $300, she promised 90 minutes of what she has described as a discreet “legal high-end erotic fantasy service.” But the discreet part is over, after federal authorities charged her with operating a prostitution ring.

“The tentacles of this matter reach far, wide and high into the echelons of power in the United States,” Ms. Palfrey wrote in a court filing last month, as she prepared to release a list of her clients’ telephone numbers and vowed to subpoena her customers — some of whom she described as prominent Washington officials.

It is a defense strategy that had its first casualty Friday.

Randall L. Tobias, the top foreign aid adviser in the State Department, became the most prominent person on the list to be publicly identified when he resigned after acknowledging to ABC News that he was among Ms. Palfrey’s clients. The State Department’s statement on Mr. Tobias’s resignation said simply, “He is returning to private life for personal reasons.”