Last month, in a negotiated agreement, YBM pleaded guilty to securities fraud in the Federal District Court in Philadelphia. The criminal investigation is continuing, and officials said it is focusing on the role that Mr. Mogilevich and two associates played in setting up and running the company.

Like a handful of other Russian crime figures, Mr. Mogilevich is barred from entering the United States. But he has Israeli citizenship, as do several other prominent Russians involved in crime, American diplomats and intelligence officials said.

While American officials believe they have shut down Mr. Mogilevich, or at least curtailed his activities -- ''in a box,'' as a senior intelligence official put it -- they fear that there are similar schemes waiting to be exposed.

''This is just one case, but there are others like it throughout the world,'' said Jim E. Moody, a retired F.B.I. agent who headed the organized crime section for many years and was one of the first agents to begin working with the Russian police after the collapse of the Soviet Union.

In the three years between the British action and the American authorities' penetration of YBM's corporate facade, the company had raised $114 million (Canadian) on Canada's capital markets. Helped by glowing claims about sales and profits, YBM's stock soared, and Mr. Mogilevich and some of his associates sold their shares for millions of dollars in profits.

The shares were traded in Canada, attracting some American investors, while the company awaited approval for listing on the Nasdaq exchange in the United States.

''They cloaked themselves in an air of legitimacy that was beyond belief,'' said a former F.B.I. official whose job included watching Mr. Mogilevich.