Environmentalists yesterday called on Sen. Bob Graham (D-Fla.), a potential Democratic vice presidential candidate, to come out against a proposed commercial airport in south Florida, saying the expansion of the former Homestead air force base would bring development and pollution that would devastate the nearby Everglades and Biscayne national parks. The Sierra Club and Friends of the Everglades are accusing Graham of lobbying behind the scenes to assist airport developers, but publicly he has said he will wait until after the Air Force completes an environmental evaluation before making up his mind on the matter. The Clinton administration blessed the airport idea when it was first proposed by local officials, but its support has grown more tepid as environmentalists have raised complaints, and both Interior Secretary Bruce Babbitt and EPA Administrator Carol Browner have come out against the plan.