President de Ia Madrid has bent over backward searching for ways to lighten Mexicos debt burden. without confronting Washington or the banks. In fact. the United States is already acting as if it were retaliating against a Mexican moratorium. For nearly a month. for exampIe. the visa section in the United States Embassy In Mexico City has been closed because of alleged Inadequate security guarantees. For many Mexicans. the effects of this restriction are devastating. But all other problems pale In comparison to the Reagan Administrations behavior last week during a hearing on Mexico in the Senate Subcommittee on Western Hemisphere Affairs.