(Dow Jones) Portfolio managers attending the 2010 Morningstar Investment Conference in Chicago expressed their major concern in one word: debt.

"What are we going to do with all this debt?" asked Jeffrey Gundlach, chief executive of Los Angeles-based investment firm DoubleLine Capital LP. as the conference opened Wednesday.

The government is "spending like mad," and the forward value of its promises to pay is $62.3 trillion against a $14 trillion economy, Gundlach noted.

The long-term view is not that encouraging, he and others said at the conference, hosted by investment-research firm Morningstar Inc.

The debt burden requires that investors remain vigilant, Gundlach said. Investors' attitude toward debt can change very quickly, he said. "You can't go on a slow boat to China, and think that nothing is going to happen to your portfolio."

Rudolph Riad-Younes, head of international equities and a portfolio manager at Artio Global Investors, referred to the situation created by the government's stimulus efforts as the "dot.gov bubble."

"Short term, the economy can be anything you want it to be as long as rates are low and the government can keep spending," he said.

However, there are structural problems, Riad-Younes said, noting that there is a trade deficit year after year. The U.S. has to go through delevering, and address its trade problems, he said. "There is no pain-free."

Steve Romick, a partner and portfolio manager at First Pacific Advisors LLC, said that there is currently no good visibility on what is going on with the economy because it is "so jacked up" on stimulus measures, rebates, etc. He cited examples of people who are "living large" as their homes are in foreclosure.

But Riad-Younes said there are always pockets of opportunity. "For example, Western Europe is almost being priced as if it's going to disappear from the planet," he said. "Over five years, we believe it will be the best performing equity market." Nevertheless, over the shorter term, it may be the worst performing, he said.