Federal land managers have released a tentative plan to protect most of the wild but energy-rich Roan Plateau in western Colorado. The Bureau of Land Management unveiled an updated environmental impact statement yesterday for the plateau, a step toward implementing a landmark compromise between conservationists and the Bill Barrett Corporation, an energy company. Under last year’s compromise, Barrett agreed to give up most of its leases to drill for natural gas on federal land atop the plateau. The compromise settled a lawsuit filed by environmentalists who want to preserve the plateau’s forests, meadows, streams and wildlife. Attorney Mike Freeman, who represented the environmentalists, said he was still reviewing the BLM’s plan but said it was encouraging.