WASHINGTON, Aug. 20 — For years, the Bush administration has shrugged off concerns about the trillions of dollars that the United States owes to China, Japan and oil-producing countries in the Middle East, arguing that these debts give no undue leverage to foreign governments.

But at a time of global financial instability, the administration has started to worry that foreign governments are increasingly converting their dollar holdings into investment funds to acquire companies, real estate, banks and other assets in the United States and elsewhere. The fear is that these so-called sovereign wealth funds could destabilize markets or provoke a political backlash.

In response, the Bush administration is pressing the International Monetary Fund and the World Bank to examine the behavior of these funds, which control up to $2.5 trillion in investments, and develop possible codes of conduct for them. Among the proposed rules would be an obligation to disclose investment methods and to avoid interfering in a host country’s politics.

Officially, the United States welcomes all investments, except those that could compromise national security. “Money is naturally going to gravitate toward dollar-based assets because of the strength of our economy,” the Treasury secretary, Henry M. Paulson Jr., said in an interview. “I’d like nothing more than to get more of that money. But I understand that there’s a natural fear that they’re going to buy up America.”