Dr. John M. Hamilton, a Columbia psychiatrist who admitted to having a sexual affair with a female patient, resigned his position yesterday as deputy medical director of the American Psychiatric Association.

His resignation came two days after a state disciplinary panel placed him on probation for five years and forbade him from treating patients for at least a year. The state Board of Physician Quality Assurance called his conduct "unethical" and a violation of state law.

Under a consent decree with the state board, the psychiatrist waived his right to a hearing and admitted to having the affair.

A spokesman for the American Psychiatric Association, a national standard-setting organization based in Washington, noted that Dr. Hamilton's actions also violated the group's code of ethics.

"While Dr. Hamilton has been a respected member of the APA's staff and has made multiple contributions to the profession, he would have been immediately dismissed from his post had he not voluntarily resigned," said John Blamphin. "We are shocked and saddened by the circumstances leading to Dr. Hamilton's resignation, but we will not tolerate violations of our ethical code."

Dr. Hamilton, 68, has declined all comments regarding his case. He served stints as superintendent of the Spring Grove Hospital Center and the Clifton T. Perkins Hospital Center for the criminally insane. The psychiatrist also maintained a private private practice in Baltimore.