Britain warned Thursday that Al Qaeda might use new methods to carry out terror attacks, but a statement listing radioactive devices and poison gas was later withdrawn.

The confusion came as visiting Homeland Security chief Tom Ridge discussed the terrorism threat with British officials.

At first, the British government gave reporters a statement about anti-terrorism measures that listed possible methods of attack.

It said of Al Qaeda terrorists, "They may attempt to use more familiar terrorist methods, such as leaving parcel or vehicle bombs in public places, to hijacking pahing different, perhaps as surprising as the attacks in the World Trade Center, to the theater siege in Moscow."

It went on to say, "Maybe they will try to develop a so-called dirty bomb, or some kind of poison gas; maybe they will try to use boats or trains, rather than planes. The bottom line is that we simply cannot be sure."

A "dirty bomb" is a conventional explosive device packed with radioactive material that can contaminate an area without a full-scale nuclear blast.

A Home Office spokeswoman said the first version was an early draft that had not been authorized. The second version of the statement dropped the specific references. The spokeswoman, speaking on condition of anonymity, said the original statement was withdrawn because the government did not want to limit the public to thinking in terms of specific threats.

In a speech in London on Thursday evening, Ridge said America would "wrestle forever" with the impact of Sept. 11, and that the threat from Al Qaeda and other groups was "unlike any other we have faced."

Looking ahead to future risks, Ridge said, "Our enemies are working to obtain chemical, biological, radiological and nuclear weapons."

He rejected claims that America was overreacting to the terrorist threat.

"Great Britain and other European nations have been terrorized before and have survived," Ridge said. "However, the new terrorist threat is unlike any other we have faced."

Al Qaeda remains our most "immediate and serious threat," he said, even though hundreds of its operatives have been "captured or killed."

Ridge said the recent bombing in Bali, the attack on the French oil tanker, the slaying of Europeans in Pakistan and the killing of a U.S. Marine in Kuwait strongly suggest that Al Qaeda retains the capability to orchestrate attacks and to inspire sympathizers.