The president of the nation's largest shippers group acknowledged Wednesday that congressional approval of landmark legislation to deregulate the maritime industry might not occur this year.

However, he maintained it will will inevitably happen.Edward Emmett, president of the National Industrial Transportation League, said that while passage of the Shipping Reform Act of 1995 is ''virtually assured" in the House of Representatives since it is attached to the budget bill, key senators have stalled the measure in the upper house.

Addressing a Pacific Transportation Association meeting here, Mr. Emmett said that regardless of the outcome of the bill this year, history is weighing strongly on the side of deregulating the last major industry still subject to close federal regulation.

''I can't guarantee the legislation will pass this year, but there is no question it is going to happen. The maritime industry is the last bastion of old-style regulation and it is going to go away. It is only a question of when," he said.

The proposed deregulation act would eliminate tariff and service contract filing requirements; allow independent rate actions on service contracts; make service contracting confidential; and eliminate the Federal Maritime Commission and its tariff enforcement authority.

The act would retain carriers' antitrust immunity, enabling carriers to continue setting rates collectively through conferences, and would strengthen U.S. laws against unfair competition by foreign carriers. The provisions would be phased in by Jan. 1, 1998.

Mr. Emmett added that even if the deregulation bill didn't pass, "we have a fallback position of just zeroing out (the Federal Maritime

Commission). You have an agency that is fully out of control, and Congress will pull the plug on them in a heartbeat."

The deregulation act was the result of a compromise negotiated in June between the NIT League and the two largest U.S. ocean carriers, Sea-Land Service Inc. and American President Lines Ltd., but it has come under increasing attack since being introduced in Congress in August.

Small shippers, transportation intermediaries, FMC commissioners and certain foreign carriers have spoken against the proposed act, but Mr. Emmett said the opposition "of most concern" is coming from U.S. ports and longshore labor.

Those groups, led by the International Longshoreman's Association and the American Association of Port Authorities, say that deregulation could lead to a reduction in cargo moving through smaller ports because carriers will be forced to further consolidate. Deregulation could force down shipping rates by as much as 20 percent, according to some ship lines' estimates.

Mr. Emmett dismissed the argument that deregulation in itself will cause hardship for smaller ports.

''That is going to happen or not happen with or without this bill. It doesn't have anything to do with this bill," he said. "Ports have to remember that shippers are their customers, too."

In an interview, Mr. Emmett was sharply critical of federal maritime commissioners who, he said, have been effectively lobbying against the deregulation bill in violation of federal laws that prohibit lobbying by commissioners.

''There is a very serious question as to whether they have gone over the line," he said.

Others said FMC commissioners have done nothing wrong.

''I don't think there is anything illegal about a commissioner or anyone else expressing an opinion with respect to pending legislation. That is done all the time," said Robert Bourgoin, the FMC's general counsel.

Although large shippers have been pressing for maritime deregulation for years, Mr. Emmett said the current deregulation drive, the first serious challenge to the 1984 Shipping Act, came about because NIT League members felt shortchanged by the FMC's settlement with the Trans-Atlantic Agreement, the former North Atlantic shipping conference, in February.