BLOOMINGTON, Ill., May 14 (Reuters) - Europe's debt problems underscore the need for keeping U.S. interest rates low for an extended period, Chicago Federal Reserve Bank President Charles Evans said on Friday.

It was the most explicit remark by a Fed official to date that the European debt crisis is becoming severe enough to directly affect the U.S. outlook.

"The risks, obviously, with the global situation make things a little bit more uncertain than we were expecting," he said. "So, if anything, I am even more comfortable with my assessment that accommodation continues to be important."

His remarks came on a day of turmoil in markets, as investors questioned whether the continent's $1 trillion bailout package would be enough to patch things up.

Asked about the potential effect of the crisis on the United States, he said: "It will affect global demand which will influence our net export position. I'm hopeful that our exposure will be minimal to modest."

Evans expressed confidence in the rescue effort, saying he believed it would buy countries like Greece and Portugal enough time to get their budget situation in order.

"It's an aggressive, forceful and hopefully effective package," Evans said in response to questions at an event sponsored by Illinois Wesleyan University.

The official, who is not a voting member of the Fed's policy-setting Federal Open Market Committee this year, said the U.S. economy is on track to grow about 3.5 percent this year and that unemployment will likely remain stubbornly high.

Coupled with low inflation and tight bank credit, these forces should allow the central bank to keep a highly accommodative policy going for now, Evans said.

Data on Friday confirmed that at least parts of the U.S. economy are on the mend, with both retail sales and industrial production rising more than expected in April.