The freight-tariff filings and cargo-preference disputes that make up the daily business of the Federal Maritime Commission don't provide much in the way of mirth, but the staff is enjoying a few laughs over the commission's attempt to investigate the Titanic.

Actually, the inquiry is about the Titanic II, the name that a couple of San Diego entrepreneurs gave a 600-passenger ship they apparently were planning to use in a commemorative voyage to recreate--minus the disaster, of course--the trip of the great Cunard liner.

According to an official commission complaint, Terry Marler and James Beasley formed Titanic Steamship Co. and in 1981 "advertised or offered passage from U.S. ports" without having obtained the required certificate of financial responsibility.

Marler did not return a call to the insurance brokerage firm he and Beasley run. San Diego port officials say no ship named the Titanic II ever put in there.

The original Titanic sank on April 15, 1912, when it struck an iceberg in the North Atlantic on its maiden voyage. More than 1,500 lives were lost in the most famous shipwreck of all time.

Naturally, the wits at Maritime are calling the current case "just the tip of the iceberg." NO LEVITY IN LOANS, ALAS . . . There's less to laugh about in the reports from the Maritime Administration (Marad), which has become an unlikely victim of the long slump in oil drilling activity caused by the worldwide oil surplus.

The connection between Marad and the troubled oil business is not as remote as it might seem. Offshore drilling rigs and the boats that service them are constructed in shipyards, and many of them were financed through loans guaranteed by Marad.

Marad now faces the prospect of acquiring title to rigs and service boats for which there may be little market. When drillers go broke, they stop making payments on their loans. The banks that issued securities to raise the loan capital then invoke the federal guarantee, and Marad has to pay up.

To avoid foreclosure, Marad, which has more than $1 billion in rig guarantees outstanding, has begun making payments on some of the loans. In the biggest transaction so far, Marad made $1.4 million in interest payments owed by Houtech Ltd. of Houston. If the rigs ever go back to work, Houtech will repay Marad the $1.4 million, plus interest compounded at 15.8 percent a year. If drilling never resumes at its former pace, Marad may end up owning scrap steel parked in the Gulf of Mexico.

Another guarantee that went bad has forced Marad to pay $13 million owed to Chemical Bank of New York. The debt was incurred by American Atlantic Shipping Inc. to build three small cargo vessels in 1979 and 1980. The company, reportedly squeezed out of some Latin American freight routes by the national shipping lines of South American nations, couldn't make its payments, and Chemical called the loan.

The ships now are part of the National Defense Reserve Fleet, which is parked on the James River in Virginia. PROMOTED . . . Thomas W. Pross, a Merchant Marine Academy graduate who has worked at Marad since 1960, has been appointed associate administrator for shipbuilding and ship operations. Pross was formerly director of the office of shipbuilding costs.