WASHINGTON – Parents claiming that childhood vaccines cause autism should not be rewarded by the courts when the scientific community has already rejected any link, government lawyers argued Monday on the first day of a hearing in federal court.

Nearly 4,900 families have filed claims with the U.S. Court of Claims alleging that vaccines caused autism and other neurological problems in their children. Lawyers for the families are presenting three theories of how vaccines caused autism. The theory at issue Monday was whether vaccines containing the preservative thimerosal caused it.

Lynn Ricciardella, a Justice Department lawyer, said that theory has not moved beyond the realm of speculation. She said that the Institute of Medicine and the Centers for Disease Control and Prevention have rejected any link between thimerosal and autism.

"There is no scientific debate," Ms. Ricciardella said. "The debate is over."

Tom Powers, an attorney for one of two 10-year-old boys from Oregon who are serving as test cases for the thimerosal theory, acknowledged that the evidence showing thimerosal led to regressive autism was indirect and circumstantial. Still, he said, it's clear the two boys did not show any symptoms of autism until after they had received all their immunizations.

"Each of them had developed normally and typically well after their first year in life," Mr. Powers said.

If the families can convince three "special masters" that thimerosal causes regressive autism, they could be entitled to damages that cover lost income after a child turns 18 and up to $250,000 for pain and suffering.

The Associated Press