Joe Swift 04/23/97 09:05 AM Last night I saw "Murder at 1600." Among its many preposterous plotlines was one involving tunnels under the White House (which may be accessed on the Mall near the Washington Monument). The tunnels were used both for escape from and access to the White House. Joe Swift jswift @ discovery.com ---- Screen-L is sponsored by the Telecommunication & Film Dept., the University of Alabama.