Investors have turned bullish on the US while tempering their enthusiasm for China as they worry about a market bubble there, according to a Bloomberg survey.

An overwhelming majority also see a government debt default on the horizon this year, according to a quarterly poll of investors and analysts who are Bloomberg subscribers. Greece is considered the riskiest government, followed by Argentina, Russia, Ireland, Portugal, Italy, Spain and Mexico.

Sentiment toward the US investment climate has flipped in just three months. Almost six of 10 respondents are now optimistic about the US while a majority held a pessimistic outlook in an October poll. A nine-month rally in US stocks has pushed up the Standard & Poor's 500 Index 68 percent through Wednesday's close.

"There appears to be a surge in interest in the US, and it's in marked contrast to tepid attitudes only three months ago," said Ann Selzer, the president of Selzer & Co, the Des Moines, Iowa-based polling firm that conducted the survey.

"American consumers are regaining confidence, and with that alone, there should be no impediments for current business to resume the growth of the past decade," said poll respondent Drew Beatty, a commodity derivatives sales analyst with Wells Fargo & Co in Dallas.

The number of US investors who see their economy improving has steadily marched upward over the past two quarterly polls, more than doubling since July.