In Washington, it is said, a gaffe is when someone speaks his mind. Secretary of the Interior Donald Hodel spoke his mind last week -- and the laughs still have not died down. Hodel recommended against signing an international agreement to reduce chlorofluorocarbons, the ingredient in aerosol sprays believed responsible for the depletion of the earth's ozone layer. Instead, he suggested the use of hats and sunglasses to guard against the lethal sunlight of an ozoneless atmosphere. Within hours, environmentalists and other Administration officials mercilessly attacked the proposal. Hodel, hatless and sans sunglasses, retreated by saying that the plan was only one of several options.