ROANOKE, Va. (AP) _ A woman whose 4-month-old son has a rare bone disease is suing the child's father to force him to donate bone marrow to save the boy's life.

The boy has osteopetrosis, which affects bone growth. The lawsuit filed Wednesday in Roanoke Circuit Court says the boy is expected to live six to 12 months if he does not receive a bone marrow transplant.

Sue Argabright asked the court to force Sanford Andrew Moore to undergo tests to determine if can donate bone marrow to the couple's son, Andy.

The lawsuit argues that Andy's biological father has ''a duty and obligation'' to undergo ''minimally intrusive tests'' and, if eligible, to donate bone marrow to his son.

John Fletcher, director of the Center for Biomedical Ethics at the University of Virginia, said forcing the father to donate bone marrow would set a bad precedent.

''Once you start to compromise donation by using force, then you have opened the door for a lot of other things, including selling organs,'' said Fletcher.

''The tradition in the United States for organ donation - including donation between relatives - is that it is a gift of life,'' said Fletcher.

University of Virginia officials said they are searching bone marrow registries to find potential donors.

The lawsuit says a biological parent is much more likely to be a suitable bone marrow donor than a stranger. However, Ms. Argabright was tested and was found to be an unsuitable donor, the lawsuit said.

Ms. Argabright issued a public appeal for donations earlier this week, saying she could not afford to pay for the transplant, which doctors have told her could cost as much as $180,000.

She said she gets no support money from Moore and has no private health insurance. It was not clear if Ms. Argabright and Moore have ever been married.

Moore could not be located for comment. Someone answering his phone Wednesday said he would be out of town until Friday.

Most of Andy's medical expenses so far have been covered by Medicaid, Ms. Argabright said, but the Virginia Medicaid program does not pay for transplants for children.

Osteopetrosis prevents the body from breaking down and reforming bone. Bones become increasingly brittle and deposits build up, putting pressure on the optic and auditory nerves.

Doctors say Andy probably will be blind and deaf by his first birthday.