In a 49-page national security report on Thursday, George Bush said diplomacy is the US preference in halting the spread of nuclear and other weapons.
But he added: "If necessary, however, under long-standing principles of self defence, we do not rule out the use of force before attacks occur - even if uncertainty remains as to the time and place of the enemy's attack."
The report, titled National Security Strategy, summarises Bush's plan for protecting America and directing US relations with other nations. It is an updated version of a report Bush issued in 2002.
In the earlier report a year after the September 11 attacks, Bush underscored his administration's adoption of a pre-emptive policy, marking the end of a deterrent military strategy that dominated the Cold War.
The latest report makes it clear Bush hasn't changed his mind, even though no weapons of mass destruction were found in Iraq.
"The consequences of an attack with weapons of mass destruction are potentially so devastating, we cannot afford to stand idly by as grave dangers materialise. The place of pre-emption in our national security strategy remains the same," Bush wrote.
"The consequences of an attack with weapons of mass destruction are potentially so devastating, we cannot afford to stand idly by"
The report had harsh words for Iran. It accused the government of supporting terrorists, threatening Israel and disrupting democratic reform in Iraq. Bush said diplomacy to halt Tehran's suspected nuclear weapons work must prevail to avert a conflict.
"This diplomatic effort must succeed if confrontation is to be avoided," Bush said.
He did not say what would happen if international negotiations with Iran failed.
The Bush administration is working to persuade Russia and China to support a proposed UN Security Council resolution demanding that Iran end its uranium enrichment programme.
Bush also had tough words for North Korea, which he said poses a serious nuclear proliferation challenge, counterfeits US currency, traffics in narcotics, threatens its neighbours and starves its people.
"The North Korean regime needs to change these polices, open up its political system and afford freedom to its people," Bush said. "In the interim, we will continue to take all necessary measures to protect our national and economic security against the adverse effects of their bad conduct."
Bush issued rebukes to Russia and China and called Syria a tyranny that harbours terrorists and sponsors terrorist activity.
On Russia, Bush said recent trends show a waning commitment to democratic freedoms and institutions. "Strengthening our relationship will depend on the policies, foreign and domestic, that Russia adopts," he said.
The United States also is urging change in China.
"China's leaders must realise, however, that they cannot stay on this peaceful path while holding on to old ways of thinking and acting that exacerbate concerns throughout the region and the world," Bush wrote.
He said these "old ways" include enlarging China's military in a non-transparent way, expanding trade, yet seeking to direct markets rather than opening them up, and supporting energy-rich nations without regard to their misrule or misbehavior at home or abroad.