"Some clouds of emerging protectionism have become increasingly visible on today's horizon," Greenspan said in a speech delivered in Berlin at an event sponsored by Germany's central bank.

"The costs of any new protectionist initiatives ... could significantly erode the flexibility of the global economy. Consequently, it is imperative that creeping protectionism be thwarted and reversed."

Greenspan did not single out the protectionist moves that concerned him.

The Fed chairman's comments come during a time of tensions surrounding globalization and the international trading climate. President Bush had imposed steep tariffs on certain types of foreign steel. But he lifted them in December under threat of retaliation by Europeans and other trading partners. On Capitol Hill, there have been calls by lawmakers to raise protectionist barriers, especially in dealings with China.

In his speech, Greenspan didn't talk about the the state of the economy or the future course of interest rate policy in the United States.

In a question-and-answer period after the speech, Greenspan was hopeful that the U.S. economy would eventually produce "marked increases in employment" but he didn't elaborate on the timing. The nation's payrolls grew by a minuscule 1,000 jobs in December. Although the jobless rate fell to 5.7 percent, it was because thousands of potential workers gave up looking.

With signs that the economy is gaining traction, business analysts believe that Fed policy-makers will hold a main short-term interest rate at a 45-year low of 1 percent at their next meeting on Jan. 27-28.

Thus far, swollen deficits in the United States' broadest measure of trade — called the current account trade deficit — have been "seemingly uneventful" and inflation remains subdued even as the dollar has fallen by about 25 percent against major foreign currencies since early 2002, Greenspan said.

"Inflation, the typical symptom of a weak currency, appears quiescent," he said. "Certainly euro area exporters have been under considerable pressure."