Eight environmental organizations sued the U.S. Forest Service yesterday for failing to increase the fees paid by ranchers to graze livestock on public lands. The groups say that the dramatically below-market rates charged by the USFS cost taxpayers money and lead to damage from overgrazing on 95 million acres of federally owned land. On average, ranchers in the country’s 16 westernmost states pay $13.50 per cow per month for grazing rights on private land; on public land, the rate is just $1.35 — the lowest it’s been in over a quarter-century. Peter Galvin of the Center for Biological Diversity, one of the organizations involved in the lawsuit, put it this way: “The Forest Service charges about as much to run a cow on public lands as it costs to feed a pet hamster.” The plaintiffs want the courts to force the USFS to make a final ruling on a languishing 1994 proposal to triple grazing fees.