LONDON - British and American weapons experts have returned to Libya and within weeks could begin dismantling, destroying and removing technology and materials related to Libya's once secret programs to develop nuclear and other illicit weapons, a senior Bush administration official said Monday.

The experts spent several weeks in the fall inspecting Libyan laboratories and military factories prior to the Dec. 19 announcement by Libyan leader Moammar Gadhafi that he would give up the weapons programs.

Plans are also being laid by Libyan chemical weapons scientists to incinerate tons of mustard gas agent manufactured to fill chemical bombs, the senior administration official told the New York Times. Missile programs and biological research efforts are still under scrutiny.

The U.S. and Britain have not decided how to remove any highly enriched uranium and the centrifuge machines designed to separate it from natural uranium in the manufacture of a Libyan nuclear bomb, a project that was in its early stages. The senior administration official said the illicit materials would probably be shipped to a secure facility in Britain or the U.S.

In Vienna, John R. Bolton, the American undersecretary of state for arms control, and William Ehrman, a senior British disarmament official, met Monday with Mohamed El Baradei, the director general of the International Atomic Energy Agency, and reached an agreement under which the U.N. agency will verify the destruction and removal work, an agency spokesman told The Associated Press.

However, the work of destroying or removing the illicit weapons will not be performed by inspectors from the international body, as it was in Iraq. Instead, it will be performed by American and British experts from intelligence agencies and from the U.S. Department of Energy and the national nuclear laboratories.

The senior administration official said Libya was ''in a hurry'' to dismantle the weapons programs and was eager to make a full and detailed declaration about its once-secret nuclear effort to the board of governors of the atomic agency in March.

Those declarations, along with the destruction of the weapons and their technology, will hasten the day when Libya looks to President Bush to lift U.S. trade sanctions and restore diplomatic relations with Tripoli. All are essential in the return of American oil companies.