Sen. Sam Nunn of Georgia says he sent investigators to Japan and Russia last summer to look into the nerve gas attack by a cult last March that killed 12 people and nauseated more than 5,500 in a Tokyo subway.

Mr. Nunn, a top expert on national security issues, said the attack demonstrates how vulnerable urban centers can be in the face of terrorism.

The ranking Democrat on the Senate Armed Services Committee, who recently announced he will retire from the Senate when his current term expires, also said the Aum Shinri Kyo cult had been recruiting Russian nuclear and chemical experts as part of a plan to overthrow the Japanese government.

Mr. Nunn said the group possessed a Russian helicopter and two airplanes capable of delivering chemical and biological weapons that the group had under production. The senator also said he heard reports that the cult was seeking nuclear materials and technology.

He said there is evidence the cult tested the nerve gas used in the subway on sheep in Australia.