The Obama administration today announced sweeping changes to the United States' policy on nuclear weapons and insisted that even though the new policy restricts the use of nuclear weapons, the nation's security will not be in jeopardy.
President Obama hailed the changes, which break the decades-old position handed down from the Cold War, as a "significant step forward" in fulfilling the pledge he made to "prevent the spread of nuclear weapons."
It "recognizes that the greatest threat to U.S. and global security is no longer a nuclear exchange between nations, but nuclear terrorism by violent extremists and nuclear proliferation to an increasing number of states," Obama said in a statement. "First, and for the first time, preventing nuclear proliferation and nuclear terrorism is now at the top of America's nuclear agenda."
Top administration officials stressed today that the new policy will not put the nation's security at risk.
"We are reducing the role and number of weapons in our arsenal while maintaining a safe, secure, and effective deterrent to protect our nation, allies and partners," said Secretary of State Hillary Clinton.
Clinton dubbed the review a "milestone in the transformation of our nuclear forces and in the way we approach nuclear issues."
The most controversial part of the policy announcement is the U.S. pledge to refrain from using nuclear weapons to attack any country that is in compliance with the Nuclear Non-Proliferation Treaty, even if that country has attacked the United States with chemical or biological weapons.
"This enables us to sustain our nuclear deterrent for the narrower range of contingencies in which these weapons may still play a role, while providing an additional incentive for nations to meet their NPT obligations," Obama said.
But Republican Senators John McCain and Jon Kyl expressed concern that the new policy puts the United States at risk.
In a statement, the two Republican senators said, "the Obama Administration must clarify that we will take no option off the table to deter attacks against the American people and our allies."
The policy is intended as a signal to Iran and North Korea, who have refused to stop pursuing nuclear programs, that if they continue down that path, they are taking steps that make them less secure.
"I actually think that the NPR [review] has a very strong message for both Iran and North Korea," Secretary of Defense Robert Gates said. "We essentially carve out states like Iran and North Korea that are not in compliance with NPT."
The message to these countries, Gates said, "is that if you're going to play by the rules, if you're going to join the international community, then we will undertake certain obligations to you, and that's covered in the NPR. But if you're not going to play by the rules, if you're going to be a proliferator, then all options are on the table in terms of how we deal with you."
Gates told reporters the United States will "hold accountable" terrorist states despite the new policy and will continue to go after terrorists who want to acquire weapons of mass destruction.
There is also the caveat that the United States can revisit the policies if circumstances change.
"The United States reserves the right to make any adjustment to this policy that may be warranted by the evolution and proliferation of biological weapons," Gates said, adding later that "We also recognize the real world we continue to live in."
Former Bush State Department official Nicholas Burns today applauded the new policy.
"The president is clearly signaling that we are really decades away now from the end of the cold war," Burns told ABC News. "That the real threats are…terrorist groups, and they're the renegade states like Iran and North Korea."
The response from Capitol Hill was mostly mute. The top Republicans on the House Armed Services Committee and the Armed Services Strategic Forces Subcommittee both praised and criticized the plan. Their biggest concern is that the administration has ruled out a nuclear strike against non-nuclear countries who are complying with the NPT.
"By unilaterally taking a nuclear response off the table, we are decreasing our options without getting anything in return and diminishing our ability to defend our nation from attack," Rep. Michael R. Turner, R-Ohio, said in a statement.
The president made it clear at the onset of his administration that he would work to reduce nuclear arsenals around the world.
Finalized after more than 100 interagency meetings, the policy review -- which Clinton said is the first NPR to be made public in its entirety -- states the United States will not develop any new nuclear weapons, contrary to what Gates originally recommended. The United States also will not conduct any new nuclear testing or develop new nuclear weapons.
Chairman of the Joint Chiefs of Staff Adm. Mike Mullen, however, said the United States will continue to modernize its infrastructure and bolster the development of other conventional weapons.
"We are going to want to make sure that we can continue to move towards less emphasis on nuclear weapons," President Obama said in a New York Times interview published today, to "make sure that our conventional weapons capability is an effective deterrent in all but the most extreme circumstances."
Today's announcement comes at the beginning of a week and a half devoted to denuclearization, with the expected signing of the U.S.-Russian arms treaty in Prague Thursday and the multi-nation nuclear security summit next week in Washington, D.C.
Obama is scheduled to sign the nuclear disarmament treaty Thursday with Russian President Medvedev. The new arms-control agreement with Russia replaces the Strategic Arms Reduction Treaty (START) that expired Dec. 5. The Obama administration, including Clinton and Gates, had been intensely working on the negotiations on the new arms-reduction treaty for the past year.
ABC News' Jonathan Karl contributed to this report.