Galloway was quoted as saying an attack on Blair that caused no other casualties would be a justifiable response to Britain's support for the 2003 U.S.-led invasion of Iraq.
"It would be entirely logical and explicable, and morally equivalent to ordering the deaths of thousands of innocent people in Iraq as Blair did," the monthly GQ magazine quoted Galloway as saying.
However, if he knew anyone was planning such an attack, Galloway added, he would tell police.
Galloway, currently in Cuba, verified the accuracy of his comments in a statement posted on the Web site of his political party, Respect.
"I think it's best that we say nothing. We may say nothing, but we think plenty," Blair's official spokesman, who speaks only on condition of anonymity, said by telephone from Washington, where Blair met with President Bush.
Galloway was kicked out of Blair's Labour Party in October 2003 for urging British soldiers not to fight in Iraq.
He later founded his party and won a new seat in the House of Commons in 2005, representing an east London suburb with a large Muslim population. During his campaign, he denounced the invasion of Iraq and called for the withdrawal of coalition troops.
Galloway defended his comments in a statement on his Web site and said it would be possible for those in Iraq who had "seen their country invaded" to construct a moral justification for the killing of Blair
"But I've made my position clear. I would not support anyone seeking to assassinate the prime minister," he said.
Menzies Campbell, the leader of Britain's third-largest political party, the opposition Liberal Democrats, said Galloway's comments risked "providing encouragement" to a would-be assassin.
"No politician, ever, by act, word, or deed, either expressly or by implication, should give any support to the notion that violence might be justified," Campbell said in a statement.
Galloway spent three weeks last year starring on the reality TV show "Celebrity Big Brother" and was ridiculed for scenes in which he lapped up imaginary milk and purred like a cat.
His decision to participate in the program, away from his duties in Parliament and alongside a topless model, an androgynous pop singer and former NBA star Dennis Rodman, resulted in criticism from constituents and lawmakers.
In his magazine interview, Galloway claimed to been the best fighter at his school, and said he would like to go a few rounds with both Blair and Bush.
"I'd take them both at once," Galloway said.
"That's what really upsets me. They are the sort of men who are ready to fight to the last drop of other people's blood. They couldn't personally punch their way out of a paper bag. They send other mothers' sons to their death, and I find them both deeply repugnant," he said.
Last May, Galloway called a congressional subcommittee "the mother of all smoke screens," after he traveled to the United States to deny accusations he had profited from the U.N. oil-for-food program.