PHILADELPHIA (AP) _ An orthopedic surgeon who operated on more than 1,000 people during the past six years has tested positive for the AIDS virus, Mercy Catholic Medical Center announced Wednesday.

The hospital said it notified the doctor's 1,050 patients by registered letter, sent Tuesday, and offered them free counseling and AIDS testing.

''Despite stressing the very low risk of HIV transmission, the anxiety of these patients will be great,'' said Thomas F. Toomey Jr., senior vice president.

Mercy Catholic went to court to get a list of the doctor's patients, according to spokeswoman Lisa Cianciulli.

The doctor, who was not named, refused voluntarily to provide a list of his surgery patients at Mercy Catholic's two hospitals, Fitzgerald Mercy in Darby and Misericordia in West Philadelphia, Cianciulli said.

Delaware County Court issued the order last week, she said.

The doctor, who joined the medical staff in 1985, notified Mercy Catholic of his infection at the end of July. He has performed no surgery since then, hospital officials said.

A patient's chance of contracting the infection from a doctor carrying the AIDS virus is 1 in 83,000 for each hour of surgery, according to a new estimate to be published Thursday in the New England Journal of Medicine.

Jeff Flood, president of the Delaware Valley Hospital Council, said the risk of AIDS transmission in a hospital is minimal. Hospitals for years have followed ''universal precautions'' prescribed by the federal Centers for Disease Control to protect patients and doctors, he said.

Jane Shull, an AIDS activist with ACT UP, said Mercy Catholic has produced no evidence the doctor ever violated procedures, giving the hospital no justification for sending out the mass mailing.

''The hospital has decided to join the side of hysteria rather than be rational about it,'' she said. ''This is not only wrong, it's dangerous. It only persuades health care workers not to seek treatment.''

There have been similar cases in Pennsylvania and around the country involving doctors who had AIDS or tested HIV positive. The only known instance of a doctor infecting patients is the case of the Florida dentist who had AIDS.

In January, the American Medical Association and the American Dental Association recommended that doctors and dentists with the AIDS virus either not perform invasive procedures or reveal their infections to patients.

Mercy Catholic has set up a toll-free hot line to provide information and answer questions about AIDS. The number is 1-800-438-7738.