ABC News, apparently in a rare leak from the Supreme Court, reported last night that the justices today will strike down, 7 to 2, the key automatic triggering provision of the Gramm-Rudman-Hollings budget-balancing act.

ABC Supreme Court correspondent Tim O'Brien said that while he had not obtained a copy of the opinion, he had been told of its contents, including that it is authored by Chief Justice Warren E. Burger with an important concurring opinion by Justice Sandra Day O'Connor.

The ABC report, if accurate, represents a rare breach in the secrecy that traditionally surrounds Supreme Court rulings before their release.

The Gramm-Rudman-Hollings act sets a series of targets for reducing the deficit over five years. When those targets are not met, the law automatically triggers the budget cuts necessary to achieve the target, based on calculations provided by the Office of Management and Budget, the Congressional Budget Office and the General Accounting Office. The GAO -- headed by the comptroller general, who is an employe of Congress -- would certify the final results and report them to the president, who would be required to make the cuts.

ABC said the court ruled that the role of the comptroller general in the Gramm-Rudman-Hollings legislation violates constitutional separation-of-powers principles.

A special three-judge federal panel, set up by the law to consider Gramm-Rudman-Hollings' constitutionality, declared the key triggering mechanism unconstitutional Feb. 7 on the same grounds. The lower court panel said that because the comptroller general is a creature of Congress, he cannot exercise budget-cutting responsibilities that are the province of the executive branch.

The law, the rest of which would remain in effect, contains a fallback provision under which the OMB and the CBO would continue to calculate the necessary cuts, but they would not be triggered automatically. Congress would have to pass a joint resolution requiring the cuts, and it would have to be signed by the president.

Most observers have said they believe that striking down the enforcement mechanism would render the law toothless, although there would be tremendous pressure on a deficit-weary Congress to agree to the cuts.

Advance word of several Supreme Court actions leaked in the late 1970s and again in 1981, prompting an inquiry by Burger. In one instance, a Supreme Court print shop employe was transferred to another job.

O'Brien's report was not seen in Washington and other East Coast cities because it was preempted by the U.S. Open golf tournament.