Without approval or knowledge of the Federal Power commission, Texaco Inc., has been burning enough natural gas at one of its refineries in Texas each year to heat 523,000 homes.

The company, in a telegram replying to a commission inquiry, disclosed Mar. 8 that it has been sending 172 million cubic feet of gas daily from federal lands it leases off the Louisiana coast to its refinery facilities in Port Arthur, Tex. Since 1964, the company estimated, it has delivered 580 billion cubic feet to the refinery.

In New York City, a Texaco spokesman said that the company "has complied with all requirements of the FPC in seeking and obtaining approval to transport" the gas.

The Natural Gas Act of 1938, permits transportation of gas from public offshore lands only after the FPC has certified approval, congressional sources said.

In 1964, the sources said, the commission authorized Texaco to carry gas in the Sabine Pipeline, a subsidary, from onshore Louisiana to Port Arthur.

But, they said, Texaco's certification does not cover construction of facilities to bring to the pipeline gas the company produces in its enormous Tiger Shoal and Lighthouse Point field offshore. Nor does it cover transportation of the offshore gas through the Sabine line to Port Arthur.

The Texaco disclosure is expected to spur inquiries by the commission and by two House Commerce Committee units.

One of them, Subcommittee on Oversight and Investigations, heard testimony last month from its own investigators that Texaco had dedicated to interstate commerce only 45 per cent of the proved reserves in the two fields, while holding 55 per cent for its own, uses.

To accomplish this, Texaco told the subcommittee, it dedicated to interestate commerce only that gas produced at specific depths. The FPC certification permits this.

After the hearing, the staff of the Subcommittee on Energy and Power asked the commission to seek information from Texaco about the movement of gas from the two fields to Port Arthur.

Agency and Capitol Hill sources expressed concern at the possibility that many large producers may be doing the same thing as Texaco, thereby unilaterally taking huge amounts of gas for themselves without FPI knowledge or permission.

The sources also speculated that this practice may have been an important contributor to the severe winter gas shortage that plagued the Midwest and Northeast.

Energy subcommittee chairman John D. Dingell (D-Mich.) told a reporter he will ask the subcommittee to consider seeking a Justice Department determination whether the Natural Gas Act, and possibly antitrust laws as well, have been violated.

He also hopes to have the Interior Department establish whether producers owe the government royalties for gas diverted to their own uses.

In addition, Dingell said, he hopes to hold hearings soon on whether specific legislation is needed to prevent producers from taking for themselves gas from the public domain.

The Texaco spokesman, contending that the firm had complied with FPC requirements, said that the FPC in 1964 had authorized Sabine Pipeline to "transport Texaco's own produced gas" from an extraction plant near Henry, La., to Port Arthur.

Texaco pledged to the agency that it would provide the pipeline subsidiary with all the gas needed at Port Arthur until 1984, the spokesman said. To fulfill the pledge, Texaco legally committed supplies from the offshore fields, he said.

In January, 1976, FPC sources revealed that without FPC knowledge or authorization, Tenneco, Inc., a major Houston-based conglomerate, had for 11 years allowed industries in Louisiana to burn large quantities of gas needed by Midwestern and Northeastern consumers.

The arrangement -- discovered accidentally by the FPC -- involved two subsidiaries, Tenneco Oil Co., a gas producer, and Tennessee Gas Pipeline Co., an interstate facility, and ultimate customers in Louisiana including a Tenneco refiner and a chemical company.

The agency staff recommended prosecution of Tenneco, but the commission rejected it.

In recent filings with the FPC and the Securities and Exchange Commission, Tenneco said that an internal investigation had unearthed sales of about 100 million cubic feet of gas a day since 1965 by its interstate pipelines, Tennessee Gas, to an intrastate affiliate, Channel Industries Gas Co.

Channel sold the gas -- which had come from public lands and was committed by contracts to interstate customers -- to a Texas refinery which paid far more for it than is permitted under federal controls on interstate sales.

The sales "may have failed to meet all regulatory requirements," Tenneco acknowledged.