Texaco Inc. is reaping a harvest of an estimated $373 million as an ironic consequence of a 1977 U.S. government ruling that it knowingly violated a federal law for 11 years by diverting a vast amount of natural gas from public lands to its own use.

As a result of the ruling, Texaco agreed to "pay back" 208 billion cubic feet of gas - enough to supply 1.7 million homes for a year. The company, which illegally kept the gas from interstate pipelines, consented to sell the pipelines an equal quantity of fuel -- from nonfederal lands -- over 10 years.

Experts who asked not to be named said the settlement will increase Texaco's gross by at least $373 million because the prices it is allowed to charge for the replacement gas are several times higher than the prices that prevailed during the diversion period, 1967 to 1977.

In addition, the Federal Energy Regulatory Commission (FERC) appears finally to have removed any possibility of a criminal prosecution for Texaco's diversion.

This result is the product mainly of a settlement negotiated with Texaco by the old Federal Power Commission, FERC's predecessor, in July 1977 when there was no expectation that the oil company would have a financial bonanza.

Later, Rep. Andrew Maguire (D-N.J.) sought a rehearing, causing the settlement to be suspended temporarily. But FERC, reluctant to break continuity with the FPC in a matter of this kind, rejected his petition in February 1978 and, except for certain modifications, reinstated the settlement.

Last week, Sen. Howard M. Metzenbaum (D-Ohio), chairman of the Senate antitrust subcommittee, who had criticized the FERC for failing to take strong enforcement action against oil companies alleged to have made hundreds of illegal diversions of interstate gas to refineries, protested the Texaco settlement in a letter to FERC Chairman Charles B. Curtis.

Texaco's "clear violation of the law" didn't lead FERC to impose "any meaningful sanction," Metzenbaum wrote. Instead, FERC is letting Texaco "keep hundreds of millions of dollars that belong to the consumer," he told Curtis.

The letter made no suggestion as to what FERC might do now. In a phone interview, however, Metzenbaum said he wants FERC to find a way to reopen the case and do something about a settlement he denounced as "meaningless" and "totally ineffective."

A commission source said Metzenbaum could petition to reopen the case.

The FERC souce said the settlement apparently did not seem out of line to the FPC three years ago. The main reason he cited: no one knew in July 1977 that Congress, late in 1978, would pass the Natural Gas Policy Act (NGPA) to increase gas prices sharply and, starting in 1985 -- Texaco's next-to-last repayment year -- lift all controls on gas from most wells drilled after February 1977.

A Texaco spokesman said the company sees no reason to reopen the case and would oppose it. He emphasized that the settlement was approved by two commissions and was not challenged in the courts by intervenors.

In addition, he said, "Texaco should be aable to say, 'enough is enough,'" particularly because of its need to do its energy development planning on the basis of ground rules that aren't "continually shifting."

The $373 million estimated increase in Texaco revenues is based on an assumption -- possibly conservative -- that the company will get an average wellhead price for the replacement gas of $2 per 1,000 cubic feet (mcf), for a total of $416 million. Only $43 million would have been yielded by the prices during the diversion period, which averaged 19.5 cents to 21.375 cents per mcf.

Under the settlement, Texaco was free to charge national market prices, which in 1978 ranged from 53 cents to $1.51 per mcf. But the NGPA mandated sharp price increases, even for gas from existing fields when gathered by new wells. The price for gas of this kind reached $2.17 per mcf on Feb. 1 and $2.20 April 1.

As to criminal prosecution, the FPC's deputy general counsel, Robert W. Perdue, unsuccessfully had urged the commission in 1977 to refer the case to the Justice Department, saying Texaco had committed a "willful and knowing violation" of the Natural Gas Act of 1938.

FERC, in rejecting Maguire's petition for rehearing, said a referral to the Justice Department might have "symbolic value," but concluded "that the public interest would be better served by the adoption and implementation of a settlement producing major tangible benefits for gas users in large portions of the country."

Finally, in October 1978, FERC modified the original settlement, which Texaco had proposed, and approved it.

Restoration of the diverted gas is "an effective set of sanctions," FERC said. By contrast, Metzenbaum told a reporter the Texaco episode is a reminder that in Democratic and Republican administration alike, "corporate crime never does seem to merit the kind of hard-nosed approach that is given to welfare cheats and petty criminals." Texaco has denied any wrongdoing.

Last May, Metzenbaum, in a letter to Curtis, cited FERC's purported "reluctance . . . to refer violations to the Justice Department." But, Curtis said FERC's record in its first 18 months in existence "deserves public commendation, not condemnation."

Metzenbaum aide James Phillips, after analyzing Curtis' response, charged in private memos to the senator that Curtis had discouraged the agency's enforcement office from suggesting criminal prosecutions of any of hundreds of illegal diversions of gas.

Although portions of the memos leaked into the Federal Times, Metzenbaum and Phillips declined to release copies. Last week's letter from Metzenbaum to Curtis followed inquiries by The Washington Post.

The gas diversions involved offshore Louisiana, where Texaco and its Sabine Pipe Line subsidiary, authorized by the FPC in 1964 to take gas from the federal domain for sale to interstate pipelnes, diverted it instead to the Texaco refinery in Port Arthur, Tex.