Thursday’s comments marked the first time that Poland officially publicly criticised Washington's main justification for invading Iraq and for winning support from European allies, including Britain and Spain.
"That they deceived us about the weapons of mass destruction, that's true. We were taken for a ride," said Kwasniewski.
However, he argued that it made no sense to pull US-led occupation troops out of Iraq.
Poland heads up a 9000-strong multinational force occupying a swathe of Iraq south of Baghdad.
Warsaw itself has the fourth-largest contingent in the occupation, with around 2500 soldiers.
Kwasniewski was speaking days after Spain’s prime minister-elect Jose Luis Rodriguez Zapatero said Madrid would withdraw its 1300 soldiers from the Polish-led contingent by 30 June, unless the United Nations took over administration of Iraq.
The Polish head of state questioned the wisdom of pulling foreign troops from the strife-torn country, saying such a move could have a counter effect.
"What would be the point of pulling the troops if it meant a return to war, ethnic cleansing and conflict in neighboring countries," he told a group of visiting French journalists.
"If we protest against the United States' dominant role in world politics and we withdraw our troops knowing they will be replaced by US soldiers, what would be the point of such a move?" he questioned.
He said he was disappointed by the new Spanish government's threat to withdraw its soldiers.