Clinton said on Friday the United States could not be sure that a military strike would destroy Iran's nuclear program, and he noted that Iran's population is three times larger than Iraq's.
The former president made his comments in answer to audience questions following a 45-minute lecture on the Kansas State University campus attended by about 9,000 people.
His remarks touched on a wide range of topics, including the need to improve health care and the economy in the United States and alleviate poverty abroad.
His comments about Iran came as officials from the United States and other major powers have been discussing imposing new sanctions against Iran over its refusal to suspend uranium enrichment.
Different kettle of fishThe UN Security Council imposed sanctions in December, but the Bush administration has not ruled out military action.
"We should be talking to the Iranians. Attacking them is a whole different kettle of fish," Clinton said.
He argued that two-thirds of Iran's population wants a moderate government and that sanctions could have some influence on the nation's powerful clerics.
"We may not have to go to war, and we may not have a disaster," he said.
"You need to talk to everybody before you bomb them. In other words, if you're going to fight with somebody - I don't care what you don't have in common - you should talk first," he added.