The United States Mint, concerned that rising metal prices could lead to widespread recycling of pennies and nickels, has banned melting or exporting them, The New York Times reported Thursday.

The Mint is also testing dozens of cheaper alternative metal compositions in the expectation that Congress will mandate a change when it meets in the new year.

According to calculations by the Mint, the metal value of pennies, which are made of copper-coated zinc, is now more than one cent. The metal value of 5-cent coins, made from a copper- nickel blend, is up to 7 cents. Adding in the costs of manufacturing means the Mint now spends 1.73 cents for every penny and 8.74 cents for every nickel it makes.

Until 1982, pennies were made of 95 percent copper. The commodity metal value of one of those coins, which still make up a large percentage of the pennies in circulation, is 2.13 cents, according to the Mint.

If even 1 percent of the 150 billion pennies and 20 billion nickels in circulation were claimed for salvage, replacing them would cost taxpayers 43 million, the Mint estimates.

In an interview on Tuesday, Edmund C. Moy, director of the Mint, said officials were aware of only a few people asking if it was legal to melt coins for their metal value. Without the ban, which takes effect tomorrow, it would be.

The new ban also forbids exporting pennies or nickels in any significant quantities. While the Mint is not concerned about tourists' pocket change or numismatic collections, it wants to block wholesale export of coins to countries where recycling them for their metal content could be economically viable.

Penalties for violating the ban can include a 10,000 dollars fine and up to five years in jail. "We want to make it clear to anyone considering this that it's not worth it," Moy said.