A unanimous Supreme Court ruled Tuesday that states may not regulate the sale of securities by interstate gas pipeline companies.

The justices held that the Federal Energy Regulatory Commission has exclusive rights to regulate the financial decisions of pipeline companies as a consequence of its regulatory authority over rates and facilities.The decision strikes down a 1909 Michigan law requiring gas companies deriving more than 5 percent of their consolidated gross revenue from operations in-state to submit plans to issue securities for mandatory approval by the Michigan Public Service Commission.

ANR Pipeline Co. and ANR Storage Co., both subsidiaries of American Natural Resources Co., have their principal place of business in Michigan.

The pipeline purchases gas from Texas, Oklahoma and other producing states and distributes it in Michigan and Wisconsin. ANR Storage operates natural gas reservoirs in Michigan for transfer of gas to out-of-state customers.

The companies filed suit in federal court arguing that federal law pre- empts the Michigan act and they have the right to market securities without state approval.

The Sixth U.S. Court of Appeals declared that the Michigan statute is pre- empted by federal law and the Supreme Court upheld that decision Tuesday.

Justice Harry Blackmun explained that the Federal Energy Regulatory

Commission occupies the field because it examines a pipeline company's capital structure in order to determine a reasonable rate of return.

A natural gas company's capital structure is related directly to the rates FERC allows it to charge, Justice Blackmun declared.

He noted that the commission has extensive regulations requiring a statement of the plans for financing a proposed facility and a detailed description of any proposed securities issuance.

The federal agency also has the power to prevent abandonment of service and require uniform accounting, the justices pointed out, and federal rate regulation allows the agency to address directly any unduly leveraged, unduly risky, or unduly capitalized investments.

If the state agency ever denied a natural gas company the right to issue securities for a project approved by the Federal Energy Regulatory Commission, there would be interference with federal regulation, the justices said.

In other business Tuesday, the Supreme Court ruled against the Internal Revenue Service in declaring that paper corporations, which act as agents for partnerships in states that allow only corporations to borrow money above usury ceilings, cannot be substituted for the partnership as true owner by the IRS.