The Treasury Department has ordered a halt to the delivery of thousands of Cuban newspapers, magazines and other publications on grounds that their American subscribers have not been properly licensed to receive them.

The shipments, primarily copies of Granma, the Cuban Communist Party newspaper, and Bohemia, a weekly magazine, have been stacking up in Boston since mid-May when Customs Service officials began impounding them.

Officials at Treasury insisted yesterday that they were simply enforcing longstanding but long-ignored rules under a 1917 law barring trade with designated foreign countries during a period of national emergency.

Treasury spokesman Robert Levine said the move was "occasioned by the fact that the Cubans started sending a large number of documents through Canada into Boston instead of different routes, such as Miami, that they had used in the past."

As a result, about 30,000 periodicals and other publications had piled up in Boston, perplexing officials there. When they notified the Treasury Department, officials in Washington decided to start enforcing the Trading With the Enemy Act, which was invoked in 1962 to start the 19-year embargo on trade with Cuba. Although newspapers are not specified in the embargo, the law says they cannot enter the United States unless the importer obtains a license from the Treasury's Office of Foreign Assets Control.

This has provoked protests from a number of subscribers who resent having to register with the federal government in order to obtain a newspaper.

Harold A. Mayerson, a New York lawyer consulted by some subscribers, charged that the government's application of the restrictions to publications were unwise and, "I think, unconstitutional."

"It has a definite chilling effect on people exercising their First Amendment rights," he told a reporter. He recalled the case of a New Jersey schoolgirl who found herself subjected to an FBI national security investigation for sending the Socialist Workers Party a letter to obtain information for a high school project.

Treasury officials claimed that readers can still obtain the publications, without getting a government license, from any one of three organizations in this country that are licensed to receive them: Tricontinental Imports, the Center for Cuban Studies and Circulo de Cultura Cubana, all based in New York City.

It appeared unlikely, however, that they could handle the volume. The administrator of the Center for Cuban studies, Naomi Friedman, said yesterday, for instance, that her organization gets only about 15 copies of the weekly English-language version of Granma and about 15 copies of Bohemia each week.

"We give them away when we get them, except for a couple of copies that we keep for our library," she said.

Mayerson emphasized that "to the best of my knowledge, there are no retailers in this country selling Cuban publications." He added that the Treasury Department insists, as a condition for granting an import license, that the American subscriber not pay for the publication.

Levine said this was largely correct. Only "scholars, researchers, journalists, or scientists working on projects listed by the National Science Foundation or the Library of Congress" can obtain a government license permitting them to pay for the Cuban publications they want.

"Anyone else who gets material from Cuba," Levine added, "can get a license for it if he can get it for free."

The impoundment came to public attention after their Customs Service sent out a sample of 100 "notices of detention" to various addressees.

"They got enough answers to make them realize there were a lot of subscribers who did want the material," Levine said. "So now they're about to send out a letter to all addressees explaining what they have to do to free up the mail if they don't have a license already."