The chairman of Texaco Inc., the nation's third largest oil company, said yesterday his firm has been approached by investment bankers and large shareholders of Marathon Oil about the possibility of stepping in to help fend off Marathon's takeover by Mobil.

United States Steel, which has said it is in the market for acquisitions in fields including energy, was also rumored to be involved in discussions with Marathon about intervening as a "white knight" to block the proposed Mobil acquisition. U.S. Steel would not comment on those reports.

Meanwhile, the takeover fight continued to be played out in courtrooms in Ohio where Marathon is attempting to win an injunction against the merger on antitrust grounds and where Mobil is trying to block legal and legislative attempts to keep its hands off Marathon. Mobil is the country's second largest oil company; Marathon is the 17th largest.

Marathon had little to say yesterday about its attempts to find another company to counter Mobil's offer. A spokesman said the company would not make any comments about possible approaches to Texaco by its investment bankers and shareholders, nor would it discuss contacts with other companies.

Marathon has said that Mobil's $85-a-share offer and ultimate purchase price of approximately $5.1 billion are inadequate, and Mobil Vice President for Public Affairs Herbert Schmertz has said that Marathon was "so underpriced, a really good buy."

According to sources, Mobil estimated Marathon's liquidation value at $11 billion and its per-share liquidation value at $188. Per-share prices offered in takeovers are generally below liquidation values.

Mobil would not comment on the accuracy of those figures. "As usual, the Washington Post is making the mistake of relying on leaks," the company said in a statement. "Material submitted to the Federal Trade Commission is specifically confidential."

Texaco chairman John K. McKinley said at a company presentation to securities analysts that his company has been contacted by several investment bankers offering their services. "Other invesment bankers have contacted us on behalf of Marathon," he said. "We have also been contacted by large shareholders of Marathon."

It was not clear whether those contacts were made with the blessings of Marathon management. "Other than recognizing these contacts we have no speculative comments concerning Marathon," McKinley said.

He said that Texaco prefers to explore for reserves rather than to buy them. But he added, "We are cognizant that there is a price at which the purchase of known reserves in the ground is preferable to the risk of exploration. Thus both routes for reserve additions are receiving attention."

In still another development, Stephen C. Mahood, vice president of Sedco, a Dallas-based oil exploration firm which is a 7.5 percent shareholder in Marathon, said that Sedco may revive an offer to buy Marathon if Mobil is blocked by the courts.

Sedco, which acquired a substantial holding in Marathon and made its own offer to buy the company which was rejected, has an obvious interest in seeing the price of its Marathon stock bid up. Details of Sedco's first offer have not been disclosed, but Mahood said that $100 a share was "in the right ballpark."

Mobil won a legal victory yesterday. A federal judge in Columbus, Ohio, issued a temporary restraining order blocking implementation of a bill rushed through the Ohio legislature designed to bar the merger. The ruling restrains enforcement of the law, which Mobil said is unconstitutional, until Nov. 30.