In a move that some coin collectors fear could eventually make it difficult to pursue their passion, the United States government has imposed import restrictions on ancient coins from Cyprus. It is the first time the United States has limited trade in a broad category of coins as part of an effort to guard the cultural heritage of another country.

The new rules, which were adopted last week and went into effect on Monday, would essentially bar the importation of any ancient coin from Cyprus unless authorized by the Cypriot government. The limits are part of a broader agreement between the United States and the Republic of Cyprus to extend for five years existing restrictions on the import of pre-classical, classical and Byzantine art and artifacts from the island.

The new rule is only the latest development in a debate involving archaeologists, collectors and art dealers over how best to preserve antiquities and encourage appreciation of the past.

Cyprus has said the restrictions are necessary to combat the looting of cultural and archaeological sites, particularly in the northern part of the island, which has been divided from the south since Turkey invaded in 1974.

Archaeologists frequently use coins to help them date ancient sites; they say that treasure hunters using metal detectors to look for coins often wreck potentially important archaeological discoveries.

“We are very pleased coins have been added to this,” said Cyprus’s ambassador to Washington, Andreas Kakouris. “Coins constitute an inseparable part of our own cultural heritage, and the pillage they are subjected to is the same as other archaeological material.”

Numismatic associations had argued before a State Department advisory committee that import restrictions on ancient coins could not fairly be enforced. Coins minted in Cyprus were found throughout the ancient world, the collectors asserted. They said it would be impossible for customs officials to determine whether a coin came from Cyprus or elsewhere and whether it had been legitimately excavated.

Coins do not customarily carry the kinds of provenance documents that accompany other art and antiquities.

The collectors also expressed concern that the agreement would encourage other countries, including Italy, home to troves of Roman-era coins, to ask for similar restrictions. If such limits “were applied to Italy, for example, that could be quite devastating to numismatists, particularly ancient-coin collectors,” said Jay Beeton, a spokesman for the American Numismatic Association.

The Archaeological Institute of America, which wrote to the State Department in support of Cyprus’s request for new import restrictions, disputes that there was widespread dissemination in centuries past of Cypriot currency.

“Coins minted on Cyprus were very rarely taken from the island in antiquity,” the association’s president, C. Brian Rose, wrote in a February letter to the State Department’s Cultural Property Advisory Committee. “If one examines the discoveries at officially sanctioned excavations in the countries that surround Cyprus, such as Turkey, Syria, Lebanon and even Israel, one can see how infrequently Cypriot coins figure among the finds.”

But the coin collectors said they saw little reason for the State Department, which had exempted coins from previous import bans on antiquities, to suddenly reverse course.

“This decision shows that the Department of State is putting the narrow interests of the cultural bureaucracies of foreign states and the archaeological community over those of ordinary Americans who believe that collecting increases appreciation of the past and helps preserve artifacts,” said Peter K. Tompa, a lawyer who has represented numismatic groups before the Cultural Property Advisory Committee.

A State Department spokeswoman, who under the department’s rules could not be identified by name, defended the government’s decision to include coins, saying they were a key component of the “pre-classical and classical archaeological heritage of Cyprus that is subject to pillage from context and to illicit trafficking.”