Pentagon specialists made an unannounced visit to Libya last month to assess costs and options for the U.S. government to help Libya destroy its chemical weapons, a senior Pentagon official said Thursday.

James A. Tegnelia, director of a Pentagon unit known as the Defense Threat Reduction Agency, said in an interview with a group of reporters that the officials who were in Libya are writing a proposal for the State and Defense departments that will sketch out what it would take to destroy the weapons and related chemicals.

"It would be a difficult thing," he said, in part because of the location, which he did not describe in detail.

The project is part of a broader American government effort to minimize the risk of nuclear, chemical and biological weapons falling into the hands of terrorists who could use them to attack the United States.

Tegnelia did not offer details of what the U.S. team found in Libya, but he said the current estimate is that it would cost about $100 million to destroy the entire inventory of Libya's banned chemical weapons.

He said Libya, which declared publicly in December 2003 that it was renouncing nuclear, biological and chemical arms, has "tens of tons" of mustard gas as well as chemicals that can be used in the production of chemical weapons.

In order to come into compliance with the 1997 Chemical Weapons Convention, Libya would have to destroy the mustard gas as well as the precursor chemicals, Tegnelia said. The question facing the Bush administration is whether it wants to help, either with the cost or with the technical expertise it would require.

Libya became a signatory to the Chemical Weapons Convention in 2004, shortly after Moammar Gadhafi announced that he would unconditionally disclose and dismantle all programs related to weapons of mass destruction.

"In the end, meeting the Chemical Weapons Convention responsibility is the Libyan government's responsibility," Tegnelia said. "In today's world, it's not like they don't have resources to be able to do that."