Maersk Line is likely to have an even bigger impact on the trans-Atlantic liner trade than was originally expected.

A spokesman for the Copenhagen-based carrier said Friday that the new vessels it is putting into the trade can carry the equivalent of 3,900 20-foot container units, some 11 percent more than the 3,500-TEU capacity previously reported.Even that statement was greeted skeptically by industry officials. I think you can go higher than that, said one executive, who asked not to be identified.

He also expressed skepticism about Maersk's previous statements that it would not cut rates to attract cargo. Maersk has joined the conference of shipping lines that collectively sets rates on exports from the United States to northern Europe, but operates as an independent on the inbound route from Europe.

Other executives noted that vessel capacity can be flexible, depending on the weight of the cargo. In a lot of cases, vessels can hold more than the declared capacity, said Philip LaForgia, vice president, sales, OOCL (USA) Inc., general agent for Dart Containerline, one of the long-establish ed operators on the North Atlantic.

The first of Maersk's new ships, the Marchen Maersk, made its maiden voyage across the Atlantic last week. Moller Steamship Co., Maersk's parent company, is building eight other new vessels that will be brought into service between now and the latter part of 1990.

Maersk, one of the largest containership operators in the world, announced late last year that it would enter the trans-Atlantic trade, which already suffers from too much shipping capacity for the volume of containerized cargo crossing the ocean.

Birger Jurgensen, Maersk's vice president for the European service, said cargo volumes on the initial eastbound and westbound trans-Atlantic sailings are meeting expectations. The ships are not sailing full, he said, but we never anticipated them to be full.

Mr. Jurgensen, who is based at Maersk's new U.S. headquarters in Madison, N.J., declined to say how much of the cargo the line is handling thus far is under service contracts.

Such contracts entitle shippers to lower rates than are stated in the tariffs filed by the shipping lines with the Federal Maritime Commission. In return, however, the shippers commit themselves to moving certain minimum volumes of cargo over a given period of time.

The new Maersk ships also can carry 500 refrigerated containers, a Maersk spokesman said.

Until the new vessels all come on stream, Maersk is using its existing fleet to serve the trade. The ships are deployed in a route that takes them

from northern Europe to the U.S. East Coast, through the Panama Canal to Long Beach and Oakland, Calif., then to the Far East. The ships then retrace the same route back to Europe.

The new vessels have the largest operating capacity of any vessels afloat. Five new American President Lines vessels being phased into its trans-Pacific operations each will have a capacity to carry 3,800 TEUs.

The largest ships ever built, the former United States Lines Econships, are being deployed by Sea-Land Service Inc., Trans Freight Lines and Nedlloyd Lines under a vessel-sharing agreement.

Those ships were built to carry 4,400 TEUs, but the three lines have agreed not to put more than 3,400 TEUs on board. At present, nine of the vessels are operating in two separate trans-Atlantic services. The three others will be phased into service from the East Coast to the Mediterranean beginning in late May.

Below are the TEU capacities for vessels operated by other major shipping lines in the trans-Atlantic trade:

* Atlantic Container Line - 1,908 TEUs, plus 1,000 automobiles.

* Dart Containerline - average of 1,900 TEUs.

* Evergreen Line - 3,400 TEUs. * Hapag-Lloyd AG - 2,594 TEUs.

Polish Ocean Lines - 1,400 TEUs.