The survey by the University of Maryland found that 52 percent of respondents said they believed President George Bush and his aides were "stretching the truth, but not making false statements" about former Iraqi President Saddam Hussein's chemical, biological and nuclear programmes.
Another 10% said administration officials were presenting to the Congress, the US public and the international community "evidence they knew was false," the survey said.
Similarly, 56% of those polled believed the US government stretched the truth or made outright false statements about Hussein's ties to al-Qaida.
Only 32% said they thought the Bush government was being "fully truthful" about the Iraqi arsenal.
The nationwide survey of 1051 people was conducted from 18 to 25 June and had a margin of error of 3.5%. It was published on Tuesday.
The weapons of mass destruction and the Iraqi government's alleged ties to al-Qaida network were given as the reason by the Bush administration for invading Iraq.
More than three months since the start of the war, US troops have neither found any of the suspected weapons nor established the link with al-Qaida.
Meanwhile, commenting on the attacks by Iraqi resistance fighters targetting the US-led occupation forces, a former four-star US army general warned that they could be locked in Iraq for the next decade.
The general, Barry McCaffrey, who led a major and controversial attack during the Gulf war in 1991, told the BBC on Tuesday that “I think we are there for 10 years.”
McCaffrey warned of a "growing and very violent underground opposition". He said the US forces, with international reinforcements, would cope in the short term, but with two-thirds of the armed forces deployed in Iraq, Afghanistan and South Korea, would not sustain a long term presence.
The occupation forces “can't create security and stability operations by themselves”, he said. They have “to build an Iraqi police force and build a new Iraqi military...that is capable of maintaining their own security," he added.
About 26 US soldiers have died in guerrilla attacks by the Iraqi resistance since US President Bush declared the end of combat in May.