Sailing smoothly into this first week of the 21st century, it's hard to see storm clouds on the horizon. But they're out there, and one of the darkest cloudbanks is global corruption.

The problem is a bit like the piracy of 250 years ago. Back then, as now, bold entrepreneurs were pushing out the frontiers of trade. The new global economy of that time was enriching honest buyers and sellers alike. But pirates lurked in the shoals of global commerce, ready to plunder the rich cargoes.

The modern-day pirates have been on a winning streak. In Russia, for example, a group of gangster-capitalists known as the "oligarchs" has looted the assets of the state over the past decade, and even Russia's steel-jawed new acting president, Vladimir Putin, will have trouble breaking their hold. In Nigeria, the new president, Olusegun Obasanjo, is battling forces of corruption so deep and widespread that the government has trouble performing the services for which officials solicit bribes. In Asia, new leaders in South Korea, Thailand and Indonesia are trying to bust the "crony capitalism" that helped triggered the economic disaster of 1997.

The tentacles of corruption reach deep into the wealthy countries of the First World, too. The best example is the Elf scandal in France. Five years ago, a fearless magistrate named Eva Joly began probing the slush funds and corrupt relationships of France's big state-owned oil company, Elf Acquitaine. In the years since, Joly's investigation has touched former foreign minister Roland Dumas and, last month, former interior minister Charles Pasqua. The scandal has jumped to Germany, too, with evidence that Elf slush funds helped finance former German chancellor Helmut Kohl's political party.

Americans may like to imagine that we're immune from this sort of corruption. And while it's true that our Cabinet ministers don't pocket envelopes of cash from kickbacks on big arms deals, as has sometimes been the case in Europe, we're hardly immune. Indeed, our most famous bank, Citibank, seems to have been a crucial (if unwitting) money launderer for some of the world's most corrupt officials.

Citibank's role was outlined in two days of Senate hearings in November organized by Sen. Carl Levin. He detailed Citibank's "private banking" activities on behalf of what he called a "rogue's gallery" of clients, including Raul Salinas, the brother of the former president of Mexico, who's now in prison in Mexico for murder; Asif Zardari, the husband of former prime minister Benazir Bhutto, who's now in prison in Pakistan for kickbacks; Omar Bongo, president of the African nation of Gabon, whose name surfaced in the Elf bribery investigation; the sons of Nigeria's infamously corrupt former military ruler, Gen. Sani Abacha; Jaime Lusinchi, a former president of Venezuela, who has been charged with misappropriation of funds; and two daughters of Indonesia's former president Suharto who allegedly stole billions of dollars from that country.

"America can't have it both ways," Levin said. "We can't condemn corruption abroad . . . and then tolerate American banks making fortunes off that corruption."

Struggling to contain this global infestation of corruption is a little-known U.S. agency called the Financial Crimes Enforcement Network, or FINCEN, headquartered in Tysons Corner in a large office block.

FINCEN tries to keep track of money laundering partly through two forms that banks and other financial institutions are supposed to file--"currency transaction reports" whenever someone deposits more than $10,000 in cash, and "suspicious activity reports," which in theory are filed when bank employees sense a transaction may involve fraud or other illegality.

The agency, a unit of the Treasury Department, now has the names, dates and places of more than 12 million big cash deposits, and more than 325,000 "suspicious activities." But that latter definition is so loose and subjective that it often fails to catch the sophisticated "private banking" transactions that, in many cases, are just another name for money laundering. Another problem is that FINCEN's operations have been geared to fighting drug lords, rather than the broader problem of global corruption.

The new Treasury secretary, Lawrence H. Summers, has decided to make money laundering a priority of his remaining year in office. He helped write a new "national strategy" for dealing with the problem, which was issued in September. The most important change would be to include more foreign crimes--such as arms trafficking, public corruption and fraud--as triggers for banks to file suspicious activity reports. That might push our Citibanks to do a better job of questioning the source of big deposits from the Salinases and Bongos of the world. Summers will need congressional legislation to conduct this wider dragnet, and he deserves it.

The war against global corruption may be the most important battle of the 21st century. This is a struggle that really takes place in the shadows, and it involves some of the world's scariest people. The global criminals are far stronger than most people realize, and honest governments need all the help they can get.