Such strikes on the Middle East could have unleashed waves of revenge attacks against British and American troops in Iraq and Afghanistan and might have seen Iran retaliate by blocking oil supplies to the west.
Mr Bush wrote on Iran: "I directed the Pentagon to study what would be necessary for a strike." He added: "This would be to stop the bomb clock, at least temporarily."
He disclosed that his national security advisors were split over the proposed attack, with some arguing that destroying "the regime's prized project" – its nuclear facility – would help the Iranian opposition, while others feared it would stir up Iranian nationalism against the US.
The former president said he discussed the plan of attack with Tony Blair, the former British prime minister, and says he ruled out the possibility of entering negotiations with Tehran.
He wrote: "One thing is certain. The United States should never allow Iran to threaten the world with a nuclear bomb."
Mr Bush also disclosed in the book, published today, that he discussed an air strike or a covert special forces raid on an alleged nuclear facility in Syria at the request of Israel.
"We studied the idea seriously, but the CIA and the military concluded it would be too risky to slip a team into and out of Syria," he wrote.
The Israelis carried out the attack themselves in September 2007.
In the book, Mr Bush also:
• Vigorously defended the use of waterboarding, a kind of simulated drowning that was known as an “enhanced interrogation technique” by the Bush administration but regarded as “torture” by many opponents, some allies and a few internal dissenters.
• Recounts his reaction after a third hijacked plane hit its target, the Pentagon, on September 11th 2001. He writes: “My blood was boiling. We were going to find out who did this, and kick their ass."
• Discloses that he ordered the Pentagon to draw up plans an attack on Iran’s nuclear facilities.
• Describes how he considered a covert attack on Syrian nuclear facilities but decided against it when the CIA judged it too risky. Israel carried out a similar attack instead.
• Acknowledges he took "too long" to act over the Hurricane Katrina disaster that engulfed New Orleans in 2005, killing more than 1,800 people, but describes being accused of racism (many victims were black) as the lowest point of his presidency, .