In a sweeping decision that affects more than 150 million acres in the western and central U.S., the Supreme Court ruled yesterday that the Clinton administration did not violate the law in 1995 when it imposed stricter environmental regulations on the grazing of cattle and sheep on federal land. The unanimous ruling, a big victory for enviros and a major setback for the livestock industry, will make it easier for the federal government to reduce the number of cattle and sheep on public land in order to protect streams and endangered species and restore overgrazed and degraded ecosystems. The ruling ends the system under which 10-year grazing permits were renewed almost automatically and allows the purchase of grazing leases by people who have no intention of putting cattle on land, including enviro groups.