NEW HAVEN, Conn. (AP) _ The death of a hospital patient is being investigated as a possible mercy killing, and two doctors have been barred from practicing at the hospital until the review is completed, officials said today.

Dr. Viswa Nathan, a heart surgeon, was suspended Oct. 4 after the death the same day of Clarence A. Reid, 66, of New Haven, said officials at the Hospital of St. Raphael. A second doctor, a resident at the hospital, was placed on a leave of absence, the hospital said. The second doctor was not identified.

Hospital spokesman Ken Warren said today an investigation was begun because of the ''circumstances surrounding the death,'' but he would not elaborate. He said Reid's family was notified of the investigation on the day of his death.

Nathan did not want to comment on the allegations, a secretary at his New Haven office said today. She said he was referring all calls to St. Raphael's.

Reid's wife, Innebell, was quoted by the New Haven Register on Wednesday as saying she never asked Nathan to put her husband out of his suffering.

She said she took her husband to the hospital after he suffered what she thought was a stroke. Doctors found a blood clot and decided to operate, but Reid never regained consciousness after the surgery, she said.

''I never would have asked the doctor to let my husband die. My husband was a beautiful man,'' she told the Register.

Reid's death certificate says his thoracic aorta, a major blood vessel, burst.

Warren would not comment on whether the hospital believed the doctors may have acted on their own or heeded a request from the family.

Euthanasia is illegal in all 50 states, though the practice is considered common. In most cases, a doctor either withholds or withdraws a supportive treatment that might prolong life in a terminal illness.

An investigation by St. Raphael's medical board into the possibility of a mercy killing could take from a week to two months, said hospital president Daniel Rissing.

The hospital said it notified both the state medical examiner's office and the state Department of Health Services Medical Quality Assurance Division.

No doctor has ever been convicted of a mercy killing in Connecticut.