While the Clinton administration proposes charging people more to visit national parks, the National Park Service continues to lose more than $100 million a year in fees it fails to collect. According to an Interior Department audit, the agency took in $68 million in gate and campground fees at the nation's 367 parks, monuments and recreation areas last year. But another $105 million in fees went uncollected. Park Service officials disagree with the audit, estimating losses closer to $40 million. They admit, however, that entry gates and campgrounds are often not staffed because of budget cuts. Auditors pointed out that 168 Park Service units don't bother trying to collect fees, even though they are authorized to do so by Congress. At Lake Mead National Recreational Area along the Colorado River, for example, auditors said the agency could make $8.2 million a year from a $5 car entrance fee. Now no one is charged. Auditors concluded that enforcing fees would more than offset the costs of collection. A new park-fee proposal by Interior Secretary Bruce Babbitt takes a different approach. Babbitt wants to raise another $32 million a year by eliminating congressional caps on national park fees and by charging on a per person instead of a per vehicle basis.