A leading U.S.-based ship line said Monday it is resuming service to Nicaragua.

Sea-Land Service Inc., Edison, N.J., named Servicios Internacionales Maritimos, Aereos y Terrestres SA as its general agent in Managua.Sea-Land employed the same agent in 1984-85, before the U.S. government barred trade with Nicaragua in May 1985. Aura Marina Espinoza is the owner and president of the Nicaraguan company.

Sea-Land's Americas division, based in Fort Lauderdale, will serve Managua by truck from ports in two neighboring countries: Puerto Cortes, Honduras, and Puerto Limon, Costa Rica. Sea-Land ships call at Puerto Cortes every Wednesday and Puerto Limon every Thursday. On the U.S. side, the vessels call at New Orleans and Port Everglades in Florida.

''We believe that United States and Nicaraguan business(es) are eager to resume the strong investment and trade relations that existed before the 1981 suspension of American economic assistance," said Ron Gabbett, vice president and general manager, Caribbean and Central America, in the Americas division at Sea-Land.

Mr. Gabbett said the line expects to carry industrial products, foodstuffs and agricultural chemical products from the United States to Nicaragua. That trade coming to the United States will mainly comprise beef, coffee, shellfish, oil seeds, vegetables and garments, he said.

Sea-Land named William Walton, country manager, Honduras, to coordinate all Nicaragua operations.

The shipping line is a subsidiary of CSX Corp., a diversified transportation and energy company based in Richmond, Va.