In violation of a 1998 federal deadline, state and local governments are continuing to operate thousands of old underground fuel tanks that may be leaking chemicals into water supplies. Leaking fuel tanks are the No. 1 cause of groundwater pollution in the country, tainting wells and aquifers. Private industry, leery of fines and bad publicity, spent millions to meet the deadline. But many governments have taken advantage of lax enforcement and shirked their responsibilities. In all, about 85 percent of the 750,000 tanks in the country were in compliance as of March 2000, says the EPA. In Ohio, however, only 4,556 of 29,177 tanks were upgraded fully by March, and Texas has failed to report any data on compliance.