The Supreme Court yesterday cleared the way for an investigation of General Motors Corp. for possible criminal violations of federal tax law.

The justices denied without comment a plea by GM intended to end the participation of government lawyer Meno W. Piliaris in a grand jury probe that began nearly two years ago in Detroit.

Piliaris is an Internal Revenue Service regional staff attorney who had told the Justice Department that sufficient evidence existed to warrant the investigation. The department's Tax Division then requested and got the aid of Piliaris, who was sworn in as a special attorney.

The department said that Piliaris was "aware of the need to preserve grnad jury secrey," and helped to establish proceduces "to avoid improper disclosures of grand jury evidence" by IRS agents. The department said he was insulated by the government "from any participation in civil tax matters concerning" GM.

But the company, charging abuses of the grand jury process, challenged its initial round of subpoenas and sought protective orders that, among other things, would have disqualified Piliaris from participating in the investigation.

Piliaris might not be interested in investigating GM's charges of misconduct against the IRS and would have access to materials that the agency could use in civil tax matters, the company protested.

U.S. District Judge James P. Churchill ruled that the department was specifically authorized by law to appoint Piliaris and refused to disqualify him.

Last September, the 6th U.S. Circuit Court of Appeals ruled 5 to 2 against GM, holding that Churchill's order was not reviewable under a 1958 law that authorizes an appeal from an interim order in a "civil action."

A grand jury inquiry into possible criminal tax violations is, on its face, not one that should be characterized as a "civil action," Circuit Judge Gilbert S. Merritt wrote for the majority.

If there is ever an indictment and conviction, GM can raise the disqualification issue in seeking review, or it can raise it by disobeying grand jury subpoeanas, being held in contempt, and then appealing, Merritt said.

In a separate opinion, Circuit Judge George C. Edwards Jr. said that no inherent conflict of interest exists in the appointment of Piliaris, because he hasn't been shown to have "done anything except demonstrate a zealous interest in collecting federal taxes for a single client -- the United States."

In one dissenting opinion, Circuit Judge Anthony J. Celebrezze said that the majority assertion that a civil action isn't involved "squarely contradicts" language in two of the 6th Circuit's own past rulings. Agreeing, Circuit Judge Paul C. Weick wrote, "A grand jury proceeding does not become criminal as to a defendant until the grand jury returns an indictment."

The case involves an audit of GM's 1972 tax return that raised questions about the company's deductions from income of the cost of expense materials -- those used in production, such as parts for machinery, that don't become part of the finished product.

The court took other actions.

Multi-Employer Plans

To provide pension retirement benefits for workers who routinely don't have a single employer, unions have sponsored approximately 7,500 socalled multi-employer plans. About half of them are in construction, the nation's largest industry, and cover a substantial proportion of the industry's 4.7 million workers

Last May, in a case involving a pension trust created by 11 home builders' associations and the International Union of Operating Engineers, the 9th U.S. Cricuit Court of Appeals ruled that the trust is a so-called defined-bemefit plan. Thus, the court held, it is subject to the section of the Employee Retirement Income Security Act of 1974 tha tis intended to insure the payment of benefits in the events a plan is terminated before it is fully funded.

Yesterday, the Supreme Court declined to review the ruling, which, The Associated General Contractors of America said in a friend-of-the-court brief, "will cause substantial, new, and retroactive liabilities to be imposed upon the contributing employer... Most individual employers could not bear the burden..."

Meat-Pricing Industries

Without comment, the court denied a request by lowa Beel Processors, Inc., for a preliminary injunction to prevent disclosure by the House Committee on Small Business of sensitive documents it obtained from Hughes A. Bagley, who took the papers with him when the company fired him in 1975.

The committee subpoenaed and made copies of the papers for an inquiry into meat pricing tentatively set to begin in April. Meanwhile, IBP, the world's largest meat packing company, has asked the court to review a ruling in which the 8th U.S. Circuit Court of Appeals found "no basis" for compelling the committee to return its copies of the papers.