CHICAGO (AP) _ Thanks to ''a political miracle,'' a Vietnamese leukemia patient has received a bone marrow transplant that doctors say may save her life.

The operation Wednesday ended a 13-month battle to bring Thuan Quach, 42, to the United States from Vietnam for medical treatment even though the two nations do not have diplomatic relations.

''As I understand it, the Vietnamese officials had no objection to her leaving, but there was considerable problem with our own immigration people in getting her in,'' said Dr. Patrick Stiff, director of the Bone Marrow Treatment Program at Loyola University, who performed the transplant.

The saga began when Huong Quach, who owns a small beauty shop in suburban Skokie, returned to Vietnam in May 1991 to visit her sister Thuan, who had stayed behind with her husband when most of the family fled in 1979.

Huong said her older sister looked horrible, so she took her to a doctor who diagnosed the disease.

Stiff said doctors in Vietnam were unable to treat the woman's acute myeloid leukemia, and she had developed brain hemorrhages and infections, including hepatitis and a 12-inch bedsore.

In October, Stiff said, a comatose Thuan was airlifted to Singapore, where doctors cured the infections and put the disease into remission with chemotherapy. But that wasn't enough.

''The best chance of curing this type of leukemia is with a bone marrow transplant, and the best chance of a match for bone marrow is with a very close relative - and they were all in the United States,'' Stiff said.

The administration at Loyola wrote to the U.S. Immigration and Naturalization Service to plead for Thuan's admission, assisted by Huong's attorney, Michael Elliott. In December, the INS ruled that Thuan could come here. ''I think it was a political miracle,'' Huong Quach said.

In another lucky break, doctors found that Thuan's bone marrow was a perfect match with that of her brother, Truc, 29.

Huong said her sister was sitting up and comfortable Thursday, and Stiff put her chance of recovery at 70 percent. She is expected to remain in the hospital at least five weeks.

In the meantime, the family, hospital and lawyer are petitioning the INS to allow Thuan's husband and six children to immigrate here.

''Psychologically, it would be the best thing for her recovery,'' Stiff said.