CHEYENNE, Wyo. - A federal judge Monday struck down a ban on road building in one-third of America's national forests, saying the Clinton administration rule illegally designated wilderness areas.

It was the second injunction issued by a federal judge against the so-called roadless rule. The first, in 2001, was overturned in December by the 9th U.S. Circuit Court of Appeals, based in San Francisco.

Monday's decision by U.S. District Judge Clarence A. Brimmer will bring the case before the more conservative Denver-based 10th Circuit.

In a 100-page ruling, Brimmer said the U.S. Forest Service designation of 58.5 million acres of roadless areas nationwide - including 6.3 million acres in Montana - was a ''thinly veiled attempt to designate 'wilderness areas' in violation of the clear and unambiguous process established by the Wilderness Act.''

Only Congress can create wilderness areas under the act.

Jim Angell, a Denver-based attorney with EarthJustice Legal Defense Fund, said the decision appeared to block the rule nationwide, even in the 9th Circuit where it was upheld.

An ''immediate appeal'' was planned, he said.

Wyoming Attorney General Pat Crank praised the ruling, calling it a decision that ''has implications throughout the entire United States.''

Brimmer also ruled that the U.S. Forest Service violated the National Environmental Policy Act when it made the roadless rule by circumventing proper procedures and acting in ''political haste.'' He said the agency did not allow enough public input on the issue.

''It is in the province of the court under NEPA to safeguard the public by telling the government that more study is needed,'' Brimmer wrote.