An African man with family ties to Saudi multimillionaire and indicted terrorist Osama bin Laden was detained in the last several days in Senegal in connection with an Algerian terrorist cell's plan to bomb the United States over the New Year holiday, law enforcement sources said yesterday.

Mohambedou Ould Slahi is believed to be the brother-in-law of an operative in bin Laden's organization. "He clearly had some role in putting this ball in motion in Montreal, and he has connections to bin Laden's organization," said a law enforcement source. "No one has been able to say bin Laden ordered this. This is a very early stage of the investigation. We are talking about working theories here."

Law enforcement authorities are seeking Slahi's extradition to the United States, on charges not yet specified, for his role in guiding the actions of a key Canadian figure in the plot, Mokhtar Houarari, sources said. Law enforcement officials were careful to specify that Slahi has not been arrested but merely detained.

Houarari was arrested last week in Montreal and described in a New York indictment as the director of the actions of an Algerian man in Brooklyn, Abdel Ghani Meskini, who in turn was in close contact with Ahmed Ressam, the Algerian first arrested on Dec. 14 in Port Angeles, Wash. Border patrol officials found explosives in Ressam's rented car capable of detonating an explosion on the order of the Oklahoma City bombing.

The trio is part of a series of seven arrests made in Canada and the United States that link Algerian nationals, primarily from Canada, in a daisy chain of phone cell records, tattered notes and recorded conversations that authorities say together form a concerted effort to take lives in a dramatic bombing on American soil.

The FBI, Immigration and Naturalization Service, Customs Service and Canadian law enforcement have been working feverishly since Ressam's arrest to determine who his accomplices were, even though Ressam has remained silent. During extensive investigation in Canada, the identity of Slahi, who is Mauritanian by birth, surfaced. "To say he masterminded this is overstating it," said a law enforcement source. "Whether the precise plan came from him or another guy above him is just not known. It's very early."

Bin Laden has been indicted in U.S. District Court for the Southern District of New York for his alleged role in launching the bombing of U.S. embassies in East Africa. Some of the individuals arrested and wanted for questioning in connection with the Algerian New Year's plot are believed to have been trained in bin Laden camps in Pakistan and Afghanistan.

So far, there has been no connection established between the East Africa bombings and the planned New Year's attack, but the appearance of Slahi on the investigative horizon, as first reported in today's early editions of the New York Times, has bolstered theories that the Algerian cell is not acting on behalf of the Armed Islamic Group (better known by its French acronym GIA) but instead carrying out motives associated with bin Laden, who has declared war on American interests.

The GIA has been responsible for the slaughter of more than 70,000 Algerians after a military junta toppled the democratically elected Islamic party in 1992. GIA attacks outside Algeria have been limited to France in the mid-1990s, and the group has yet to claim responsibility for any terrorist act or intended attack on U.S. soil.