The Export-Import Bank yesterday postponed final approval of a controversial $289.3 million loan to an Australian airline controlled by publisher Rupert Murdoch.

Bank officials gave no immediate explanation for the action, nor would they say how long the loan to Ansett Airlines would be delayed. The airline is a wholly-owned subsidiary of Ansett Transport Industries Ltd., which is controlled by Murdoch.

Sen. William Proxmire (D-Wis.) asked the bank last week to delay the loan until the General Accounting Office investigated reports published in The Washington Post that 17 percent of the Ansett loan money was to finance "credit memorandums" in excess of the cost of the Boeing 767 jets being purchased by the airline.

The bank's board was expected to approve the laon yesterday. After their meeting, John Moore, the outgoing bank president, simply said the board would not act at this time.

Documents obtained by The Washington Post show Ansett has a $34.2 million credit with Boeing and the General Electric Co., which manufactures the engines for the 767's. In the case of the Boeing and GE credit memos, the bank apparently is financing a vaguely described list of items such as advertising, publicity and parts to "support" Ansett's planes.

There were indications that many bank officials were unaware of the credit memos in approving the Ansett loan.