The Supreme Court yesterday allowed Montana to continue capitalizing on its abundant coal resources through high taxation and said only Congress can stop such energy opportunism by mineral-rich states.

In a 6-to-3 decision, the court upheld a tax drastically increased in 1975 by the Montana legislature at the height of the nation's energy crisis. The tax, by far the highest of its kind in the nation, now is as much as 30 percent on the sales prices of coal taken from the state.

The court said Congress must resolve arguments that such taxation will promote a mini-cartel of resource-rich states free to exploit the nation's energy-poor regions.

A coalition of 200 members of Congress from 18 northeastern and mid-western states yesterday released a new study finding that such so-called severance taxes threaten to create "a kind of United American Emirates, a group of superstates with unprecedented power to beggar their neighbors in the federal system."

Writing for the court in Commonwealth Edison Co. v. Montana, Justice Thurgood Marshall avoided discussion of the potential for an American cartel and instead strictly analyzed the Montana tax as an "even-handed formula," based on the percentage of the value of coal taken from Montana mines and applied to in- and out-of-state consumers.

Marshall rejected the notion that the courts should decide the acceptable level of taxation, saying that decision should be made by the state legislatures and, if necessary, Congress.

In a brief concurring opinion, Justice Byron R. White said he agreed with the court's opinion, but "with considerable doubt," and said Montana's coal tax may turn out to be "an intolerable and unacceptable" burden on commerce between the states. But White, too, agreed that the court should leave it to Congress to relieve those burdens.

Congress is "very much aware of the nation's energy needs, of the Montana tax and of the trend in energy-rich states to aggrandize their position and perhaps lessen the tax burdens on their own citizens by imposing unusually high taxes on mineral extraction," White wrote.

Montana and other resource-righ states "do not have the political power to impose their will on the rest of the country," White said, and Congress has the constitutional authority and machinery to stop them. For now, White wrote, "the better part of wisdom and valor is to respect the judgment of the other branches of government."

Marshall noted in his opinion that the controversy about the Montana tax has not eluded Congress, where several bills were introduced last year to limit the rate of state severance taxes. The Senate subcommittee on intergovernmental relations, chaired by David F. Durenberger (R-Minn.), plans hearing July 15 on energy-related taxes, including the severance tax.

Marshall also wrote that while three-fourths of Montana coal is on federal land, the state is not blocked from imposing a tax on coal extracted from those areas. Marshall said the Mineral Lands Leasing Act of 1920 and its amendments allows states to impose unlimited severance taxes on consumers who lease federally owned property in those states.

In May, the court overturned 7 to 1 a tax imposed by Louisiana on off-shore natural gas passing through the state. The court said the tax obstructed free commerce because it unfairly targeted out-of-state consumers and did not affect Louisiana users.

Moreover, the court ruled in that case that the jurisdiction to regulate natural gas prices belonged to the federal government not the states. There is no similar regulation of coal prices.

Marshall and White were joined in the Montana opinion by Chief Justice Warren E. Burger and Justices William J. Brennan Jr., Potter Stewart and William H. Rehnquist. Justice Harry A. Blackmun filed a dissenting opinion joined by Justices Lewis F. Powell Jr. and John Paul Stevens.

Blackmun said the Montana coal producers and utilities who sued Montana should have had a chance at trial to show that revenues from the coal tax were out of proportion to state services provided to coal producers.

Blackmun accused the majority of producing a mechanical rule that would allow Montana to tax coal at "100 or even 1,000 percent of value" and would permit taxes on coal so high that Montana could eliminate all other taxes on its citizens.

Such a "startling result," Blackmun wrote, is not justified by the Supreme Court's prior rulings.

The producers and utilities went to a state court in June, 1978, seeking refunds of $5.4 million in coal taxes they had paid under protest and asked that the tax be declared invalid. Without hearing evidence, the court upheld the tax, and the Montana Supreme Court affirmed the decision.