President Clinton yesterday signed into law what was the only piece of major environmental legislation passed by Congress this year, a $7.8 billion plan to restore the Florida Everglades over the next 30 year to 40 years. The signing drew an enthusiastic Bush to the White House — that’d be Jeb, the Florida governor. Meanwhile, a federal study of what to do with the former Homestead Air Force Base found on Friday that redeveloping the base into a commercial airport would not have a negative environmental impact on the nearby Everglades and Biscayne national parks. State government and business leaders are pushing for an airport, while enviros prefer a plan to make the air force base into an office park and hotel. They still hope Clinton will side with them in his last days in office.