Of all the national park lands in the United States, none is closer to a major urban area or more beset with problems than the Everglades, a shallow, 50-mile-wide river of grass that flows south from Lake Okeechobee to Florida Bay. For more than a generation, this fragile natural wonder has been held hostage by a web of special interests -- farmers, sportsmen and about 6 million South Florida residents in need of drinking water and flood control -- that is as complex as the ecosystem itself.