A federal judge prohibited U.S. officials yesterday from enforcing key provisions of a two-year-old law that forces strip miners to restore the mountains they damage in search of coal.

The order, affecting coal mines in Soutwest Virginia, was the first permanent injunction issued in the United States declaring unconstitutional major sections of a law long sought by environmentalists to halt the scarring of Appalachia and other regions by miners.

the Justice Department is expected to appeal the ruling, issued by District Court Judge Glen M. Williams in Abingdon, Va., a small town near the center of Virginia's coatfields.

The judge's order struck down a section of the law requiring strip mine operators to restore steep mountain slopes to their "approximate original contours" after coal has been extracted. This provision has been highly controversial in the rugged Southwest Virginia coal fields, where sharp slopes are common.

Williams' order also held unconstitutional key enforcement powers granted to federal officials under the 1977 act. After a preliminary analysis of the judge's decision, federal government lawyers said the ruling apparently bars the Interior Department from issuing orders to coal mine operators to cease illegal practices. It may also prohibit them from handing out milder notices requiring miners to correct environmental violations, the lawyers said.

"He enjoined virtually all our enforcement authority," one Interior Department lawyer said yesterday.

The landmark 1977 Surface Mining Control and Reclamation Act has caused widespread controversy, pitting environmentalists against the coal mining industry. Legislation designed to weaken the 1977 act has already cleared the Senate and is awaiting House consideration.

Two other major court challenges against the constitutionality of the law are pending in Indiana and Iowa, according to federal officials no court decision has yet been issued in either state. These suits focus, in part, on a provision of the law requiring prime farming land to be restored to agricultural productivity after mining is completed.

Federal environmental officials contend that the strip mining law -- enacted after years of debate and two presidential vetoes -- is necessary to prevent flooding, landslides, soil erosion, water pollution and other environmental damage.

The strip mining industry in Virginia has complained that the law resulted in increased mining costs, forced some companies out of business and led to losses of hundreds of mining jobs. Coal officials also assert that parts of the law are environmentally unsound and charge that there have been abuses in the way federal officials enforce the regulations.

Virginia -- the nation's seventh-ranking coal-producing state -- joined with the industry in the suit challenging the federal law, arguing that the law represents an infringement on the state's constitutional rights to regulate its coal fields.

Virginia Gov. John N. Dalton -- who testified last year in court against the strip mining law -- issued a statement last night praising Williams' order. "The court's ruling removes a severe economic burden that was unreasonably placed on coal produtction in Virginia and is good news for everyone concerned with full development of our domestic energy resources," Dalton said.

The judge's order was also hailed by officials of the Virginia Surface Mining and Reclamation Association, the industry group that initially brought the lawsuit. "In effect, we have won the case -- at this stage," said John L. Kilcullen, a lawyer for the association noting the likelihood of a court appeal.

Judge Williams had initially issued a sweeping preliminary injunction against the federal strip mining law last February, but his temporary ban was later overturned by the 4th U.s. cIrcuit Court of Appeals in Richmond. wWilliams' permanent injunction yesterday appeared to be narrower, in part than his earlier ruling, despite its potentially crippling impact on federal strip mining regulation in Virginia.

A study by the U.s. gEological Survey concluded that 95 percent of the coal that could be extracted by strip mining in Virginia lay within steeply sloping mountains -- slopes rising at angles greater than 20 degrees. This was the highest percentage of any state in the country -- and indication of the significance of Williams' order for Southwest Virginia.

In striking down provisions requiring steep mountain slope to be restored to their "approximate original contours," Williams held that the requirements "are not environmentally sound and do not serve the interests of the federal government and are so burdensome on the commonwealth of Virginia as to threaten its economy."

In his 38-page opinion, the judge sharply criticized enforcement procedures used by federal strip mining inspectors, labeling them "shocking" evidence of "the power of bureaucrats to close down a legitimate business at their whim."

Williams held that provisions of the 1977 law violated both the Fifth and Tenth Amendments because, he said, they "effectively prohibit the mining of a person's private property," deprive mine operators of "procedural due process" and serve to "displace the states' freedom" to carry out what he termed "traditional functions."