Officials trying to catch accused terrorist leader Osama bin Laden and his followers have been stymied, at least partly, by the way he has apparently been able to hide his wealth and the financial transactions used to carry out a campaign of violence. Authorities are expected to seek more cooperation from financial institutions to track down the money trail.

Saudi exile Osama bin Laden is believed to have a personal fortune of more than $300 million. Some of that may have come from his family, which owns a large Saudi construction company.

Mr. bin Laden is also believed to have profited in the 1980s from his association with Afghan rebels who received U.S. funding for their insurgency against the former Soviet Union.

According to former U.S. ambassador to Pakistan Robert Oakley, Osama bin Laden now gets money from a variety of sources. "He has it from his personal wealth, but he now is able to get it from all sorts of places," he said. "There are a number of very, very wealthy Muslims who are willing to contribute to Bin Laden's organization still, and there have been before. That's his chief source, in addition to his private fortune, which he's probably diminished considerably."

Mr. bin Laden's financial network is reported to involve companies in many countries, including Tunisia, Cyprus and Switzerland. Those businesses have been accused of serving as front companies, laundering donations from his supporters in the Middle East, Africa and Muslim communities in Europe. The Cypriot government, however, has denied that Cyprus has been used as a financial haven for Osama bin Laden. And a board member of one Swiss company, Al Taqwa, denies any link to terrorism, saying instead that the company helps fund agriculture and education projects in developing countries.

Securities officials in the United States, Europe and Japan are investigating whether Osama bin Laden's organization may have profited from last week's terrorist attacks by selling large amounts of shares of reinsurance companies in advance of the planned attacks.

Eric Melby, a senior fellow at the Forum for International Policy in Washington, says finding and freezing the assets of Mr. bin Laden and his network, called Al-Qaeda, or "the base," will be difficult, but not impossible.

"As we saw from the incidents that happened here last week," said Mr. Melby, "it's likely that it was a very long, well planned operation which required substantial financial resources to keep the various teams going. So, there is money flowing out to support these people. ... And it will require I think a sophisticated effort to break into their communications networks because they clearly communicate among themselves and transfer money among themselves, and there are probably selected countries in the world that less savory characters try and do their banking in away from the rigorous regulatory oversight that exists in, say, the OECD countries."

Ambassador Oakley says the United States and other countries have been trying to track Osama Bin Laden's financial transactions, but he says the alleged terrorist leader uses unconventional methods to hide and move his money.

And Mr. Oakley adds that the U.S. government is going to expect more cooperation from banks to track the funds. "There's going to have to be changes in the laws affecting the behavior of banks and the way in which banks themselves will handle money transfers, deposits and things of this kind," he said. "There's been some improvement made, but with respect both to terrorism and narcotics trafficking in the past decade. But there obviously has to be more done. This is going to mean making some changes which the banking system, international banking system may not like."

For example, Ambassador Oakley says banks will have to get used to a higher degree of disclosure, something he says banks do now only grudgingly.

An international economics specialist at the Council on Foreign Relations, Caroline Atkinson, agrees, saying she expects new legislation designed to help the U.S. government crack down on money laundering. But for Ms. Atkinson, tighter restrictions on the banking system may still not get at the money that is transferred through unconventional means. And she points to a casual system of transactions called Hawala, often used by people in the Middle East and based on personal trust.

"I could want to pay you some money, and we could be in different countries," says Ms. Atkinson. "And I go to a third party and pay them the money, and they then instruct a colleague of theirs in your country to pay you the money. There's no bank transaction. There's no deposit in a bank. There's no cross border transaction that would suggest that we're doing what we're doing. There of course has to be the instruction going from one end of the hawala, the people that receive my cash to the people that are going to give you your cash."

Ms. Atkinson says those instructions could be by telephone, fax or personal messenger, with very little paper trail to trace.

Because of the terrorist attacks in New York and Washington, Ms. Atkinson expects that many countries - the United States, Germany, Switzerland, and others - will embark on an intense philosophical debate about how to balance their desire for privacy of financial transactions and the need to prevent criminal and terrorist activity.