Nearly half of Americans think its news media is too liberal despite the rise of controversial hard-right cable channel Fox News.
TV news channels in the US came under fire during the war on Iraq - including criticism from some of their own reporters - for their unquestioning support of the White House during the conflict.
But this criticism is not shared by viewers at home, some 45% of whom believe their country's news outlets are too liberal.
Only 14% of Americans believe the media to be too conservative, according to a poll by Gallup carried out around the second anniversary of the September 11 attacks.
"The ratings success of the Fox News channel has been based in part on its attempt to appeal to conservative viewers who feel that the more traditional news media are liberal and biased," said the report's authors, Frank Newport and Joseph Carroll.
"A majority of Americans who describe their political views as conservative perceive liberal leanings in the media, while only about a third of self-described liberals perceive conservative leanings."
But public trust in the media has collapsed since the mid-1970s, when around seven in 10 Americans said they had confidence in TV and newspaper outlets.
"This perhaps reflected public approval of the news media's role in uncovering the Watergate abuses of power," suggested Gallup.
Today, a little over half of Americans have a "great deal or fair amount" of confidence in the news media, which is less trusted than any of the three branches of government.
Only 54% had a "great deal or a fair amount" of confidence in the media, compared with 60 per cent in the president, 63% in congress and the senate, and 67% in the courts.
The findings of liberal bias will surprise observers who have criticised US news networks as being too unquestioning in their support of the government, rather than too liberal.
Fox News in particular came under fire for its "flag waving" support of the war on Iraq.
The Rupert Murdoch-owned network's patriotism was unrelenting throughout the conflict, referring to American troops on the front line as "heroes" and "liberators".
Fox's star interviewer, Bill O'Reilly, told viewers the US should "splatter" the Iraqis, while reporters railed against anti-war protesters over footage of Saddam Hussein's statue being pulled down.
The BBC director general, Greg Dyke, hit out at the "gung ho" stance of Fox News and other news channels, claiming he was "shocked" by "how unquestioning the [US] broadcast news media was during this war."
However, the Independent Television Commission threw out complaints of bias, saying it did not breach the regulator's "due impartiality" rules.
CNN's star reporter, Christiane Amanpour, said her own network was "intimidated" by the Bush administration in its coverage of the war in Iraq.
She said CNN had been "muzzled" by a combination of the White House and the high-profile success of Fox News.
In the Gallup survey, which questioned 1,025 people, around four in 10 Americans identified themselves as conservative. About the same number said they were moderate, while fewer than 20% described themselves as liberal.
Former US vice president Al Gore was said to want to launch a liberal-based news channel to challenge the growing strength of the conservative media in the US.
week he was reported to be close to signing a $70m (£44m) deal to buy cable network Newsworld International from Vivendi Universal.
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