WASHINGTON (AFP) - A US judge has ordered that a dying 10-year-old be transferred to an adult waiting list for a lung transplant, said a lawmaker who has been lobbying for the girl.

Sarah Murnaghan is critically ill with cystic fibrosis, a genetic disease that affects the airways.

She is at the top of a waiting list for children under 12, but pediatric donor lungs are far rarer than those from adults, and experts have given Sarah only a few weeks to live if doctors do not perform a transplant.

Lawmakers aware of the Murnaghan family's plight have pressured President Barack Obama's administration to assist in temporarily bending the rules to allow Sarah onto the transplant list for people 12 and older.

Senator Pat Toomey of Pennsylvania, where Sarah has been hospitalised for three months, wrote Health and Human Services Secretary Kathleen Sebelius asking her to reconsider allowing the girl to join an adult list, which would increase her chances of receiving a transplant.

"Finally, we have some positive news for Sarah and her family," Mr Toomey said in a statement on Wednesday, noting the federal judge's temporary order stopping Sebelius from enforcing the 12-and-over policy for the adult transplant list.

"Now Sarah has a chance for a lung transplant, and I plan to keep fighting for her and others who deserve to be eligible."

On Tuesday, several lawmakers pleaded with Ms Sebelius at a hearing in the House of Representatives.

While the health secretary said she "can't imagine anything more agonising" than the Monaghan ordeal, she declined to intervene or suspend the rules established by the Organ Procurement and Transplantation Network, citing medical rules and fairness to other patients.

The rules "reviewed on a regular basis are there because the worst of all worlds, in my mind, is to have some individual pick and choose who lives and who dies," Ms Sebelius said.

According to Mr Toomey, the committee responsible for emergency transplants will meet on Monday.