Mobil Corp. yesterday asked a federal appeals court in Cincinatti to block U.S. Steel Corp. from going forward with its purchase of Marathon Oil.

Mobil took the action after U.S. Supreme Court Chief Justice Warren Burger's denial of the company's emergency request for an injunction against U.S. Steel's $6.3 billion bid for Marathon. Burger denied the request because Mobil had not first sought a stay from the lower courts.

To correct the defect, Mobil yesterday went back to the court where the company's legal troubles began. First the firm asked U.S. District Judge John M. Manos to temporarily bar U.S. Steel's purchase of Marathon stock.

When Manos turned Mobil down, the oil firm moved quickly to the U.S. Court of Appeals Sixth Circuit with its request for emergency action. Manos had barred Mobil's proposed acquisition of Marathon on antitrust grounds, a ruling that the appeals court declined to overturn.

Unless Mobil succeeds in its legal maneuvers or another bidder for Marathon emerges, the steel producer may begin buying Marathon stock after midnight Jan. 6.

As of late yesterday, there had been no action by the appeals court. If the appeals court were to grant Mobil's request, it would allow Mobil time to seek a review of the antitrust question before the Supreme Court. Mobil has already requested such a review and asked the court to consider the antitrust question in the context of its agreement with Amerada Hess, under which Amerada Hess would take over Marathon's marketing, refining and transportation operations.

If the appeals court denies the injunction, then Mobil may approach the Supreme Court asking it to grant an injunction again in the short time remaining. Once U.S. Steel begins to buy Marathon stock, the fight would be over and the issue moot.