Reagan reported backing Puerto Rican statehood

President Reagan will endorse statehood for the troubled American commonwealth of Puerto Rico Tuesday, Sen. Alphonse D'Amato (R) of New York said.

Senator D'Amato said Mr. Reagan's endorsement would be an ''initial step'' which would set the stage for a change in the island's status. The Puerto Rican people would have to approve any moves toward statehood in a referendum.