WASHINGTON, Aug. 6 - A top House Democrat called on Attorney General John Ashcroft on Friday to explain why the Justice Department was letting federal officials cooperate in a Congressional inquiry into the case of Samuel R. Berger despite a current criminal investigation. The representative, Henry A. Waxman of California, the senior Democrat on the Government Reform Committee, said the department position regarding Mr. Berger, a national security adviser to President Bill Clinton accused of mishandling classified documents, was at odds with how inquiries tied to the Bush administration had been handled. "For example, in the investigation into the leak...