When Congress passed a law in 1974 to assure that the public would be allowed to comment on government antitrust suit settlements, it cited the smoke-filled-room secrecy of a 1956 consent agreement between the Justice Department and American Telephone & Telegraph Co. as an example of the need for the law.

Yesterday, U.S. District Court Judge Harold H. Greene referred to the same law as a reason he had no intention of rubber-stamping the latest settlement of the U.S.-Bell System case.

The Antitrust Procedures and Penalties Act, which cleared Congress just after the latest AT&T suit was filed, requires that any consent decree include a 60-day waiting period for public comment, a competitive impact statement by government lawyers and a list of the defendants' lobbying efforts on the settlement.

A federal judge in California cited the same law, known as the Tunney Act, in mid-November in accepting the Center for Auto Safety's contention that the Reagan administration couldn't junk a 1969 consent decree on auto emission controls.

A Justice Department spokesman said yesterday that government lawyers don't feel that the law requires them to go through the public comment period because they settled the case by modifying the old decree, not by a consent decree in Greene's court. But the department had no immediate answer on why the parties went to another judge first.

An AT&T lawyer called the disagreement a "tempest in a teapot." Justice Department spokesman Mark Sheehan called the issue a "procedural glitch." He said the department still intends to get the case transferred to Greene so he can conduct a Tunney Act review.

"In fairness to the public, even though it's not required, such a review is appropriate and necessary," he said.

Legal experts said they didn't think Greene's action threatens eventual acceptance of the proposed settlement, but a few questioned the wisdom of the parties' apparent effort to sidestep the law.

Rep. Peter W. Rodino Jr. (D-N.J.), chairman of the House Judiciary Committee, said Monday that he intended to ask Assistant Attorney General William Baxter why the parties took the "somewhat convoluted procedural approach" of going first to a federal judge in Newark to try to modify the 1956 agreement and then transferring the whole matter to Greene in Washington.

U.S. District Court Judge Vincent P. Biunno, in Newark, surprised government and AT&T lawyers and upset their plans by quickly agreeing to their motion to modify the 1956 order denying the telephone company access to unregulated markets, but delaying a ruling on the transfer to Greene.

Baxter deputy Ronald Carr told Biunno that the parties were seeking the transfer because Greene was familiar with the complexities of the current case and because it was more convenient for the government and the telephone company to make appearances in Washington.

The Tunney Act wouldn't apply to earlier settlements such as the one in Newark, and Biunno made it clear in a rambling half-hour hearing Monday that he considered the agreement in the public interest.

Thus, he signed the modification freeing AT&T from the restrictions of the 1956 settlement, but delayed the transfer to Greene. That "carries no implication of any doubt of the propriety of the transfer," Biunno said. "It appears to be authorized by law." He just hadn't completed his research on the issue, he said. The judge could not be reached for comment yesterday.