WASHINGTON — The Supreme Court is wading into a complicated immigration dispute about the status of children who have become adults during their parents' years-long wait to become legal permanent residents of the United States.

The justices said Monday they will hear an appeal from the Obama administration arguing that those children in most cases should go to the back of the line in their own wait for visas to live in this country.

The case concerns how to treat a prospective immigrant who turns 21, under a provision of the Child Status Protection Act intended to keep immigrant families together.

Proposed immigration legislation before the Senate includes a provision that would favor children who turn 21 during their parents' lengthy wait to win approval to live in the United States.