Antwerp, Belgium ? An aggressive year-long European investigation into al-Qaida financing has found evidence that two West African governments hosted the senior terrorist operatives who oversaw a $20 million diamond-buying spree that effectively cornered the market on the region’s precious stones.

Investigators from several countries concluded that President Charles Taylor of Liberia received a $1 million payment for arranging to harbor the operatives, who were in the region for at least two months after the Sept. 11, 2001, attacks on New York and the Pentagon. The terrorists moved between a protected area in Liberia and the presidential compound in neighboring Burkina Faso, investigators say.

Long accused of sanctioning illicit diamond and weapons trading, Taylor and President Blaise Campaore of Burkina Faso deny the charge, which is included in a summary of the joint intelligence findings.

The Washington Post obtained a copy of the military intelligence summary, which offers the clearest picture yet of al-Qaida’s secretive business operations in West Africa and an elaborate plot that began in 1998 to hide substantial terrorist assets in diamonds.

European and Latin American investigations also found evidence that a group of people buying diamonds on behalf of the terrorists were simultaneously attempting to procure sophisticated weapons, such as missiles that could shoot down aircraft, The Post has learned. Investigators have been unable to trace the diamonds since they left Liberia and Burkina Faso.

The diamond-buying operation appears to have been hatched in response to a move by the United States in 1998 to freeze al-Qaida assets after attacks on two U.S. embassies in Africa that were blamed on the organization. Senior European intelligence sources said they have been baffled by the lack of U.S. interest, particularly by the CIA, in their recent findings. The CIA, which in the past has downplayed reports of al-Qaida’s diamond connections, declined to comment.

In the weeks after the Sept. 11 attacks, the U.S. Defense Intelligence Agency did try to monitor the two senior al-Qaida operatives supervising the diamond trading, who were known to be hiding in an elite military camp in Liberia. Both men were on the FBI’s Most Wanted list of terrorists. The Pentagon prepared a small Special Forces team in neighboring Guinea to snatch the two, but the mission was not carried out because the team could not confirm the targets’ identities, according to sources.

The European law enforcement investigations, launched soon after Sept. 11, have focused on three people who allegedly served as conduits to the al-Qaida operatives: Aziz Nassour, a Lebanese diamond merchant; his cousin Samih Osailly; and Ibrahim Bah, a Senegalese soldier of fortune who has trafficked for years in diamonds and guns across Africa. All three deny involvement with al-Qaida or in illegal activities.

Al-Qaida’s diamond purchases were first reported publicly 13 months ago. Subsequent investigations by Belgian police and other European intelligence agencies have shed new light on the operation’s scope, its financing and al-Qaida’s extensive ties in West Africa.

Several other efforts have been under way to unravel illicit diamond trade through Liberia and its links to weapons smuggling and terrorism. A specially appointed U.N. panel of experts has studied the issue, and the Security Council in 2001 accepted the panel’s recommendation to ban international travel by Taylor, his family and senior government officials.

Much of the new evidence of al-Qaida’s diamond plot flows from the April 12 arrest here of Osailly, who is in prison awaiting trial on charges of diamond smuggling and illegal weapons sales. Osailly is involved with a small diamond importing company believed to have been used by the al-Qaida operatives. He has pleaded innocent.

In Osailly’s case, Belgian investigators say they uncovered bank records showing that the diamond company enjoyed a sudden surge in business and turned over almost $1 billion in the year before Sept. 11. Investigators also have found telephone records of calls to Afghanistan, Pakistan, Iraq and Iran.

“What we know is that al-Qaida was very active in the diamond trade, but we also know there is a great deal we don’t know,” said one senior intelligence official. “What else is there out there we haven’t discovered? What are they still doing that brings them profit? Those are the questions I worry about now.”