President Obama's decision to reverse 65 years of U.S. nuclear weapons policy and drop most of the nation's deterrence capacity has alarmed critics who say they fear that the United States will now be more vulnerable to attack from would-be nuclear nations.

By changing the policy, the Obama administration hopes the United States can focus on stopping the spread of atomic weapons to terror groups such as Al Qaeda as well as halt North Korea's nuclear buildup and Iran's nuclear ambitions, Defense Secretary Robert Gates said Tuesday in announcing the new Nuclear Posture Review.

But skeptics say the policy change will only embolden those groups and tie the U.S.' hands.

"I'm deeply concerned by some of the decisions made in the Nuclear Posture Review and the message this administration is sending to Iran, North Korea, and non-state actors who may seek to harm the United States or our allies," Rep. Michael Turner, R-Ohio, the ranking member of the House Armed Services Subcommittee on Strategic Forces, said in a written statement. "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."

"We believe that preventing nuclear terrorism and nuclear proliferation should begin by directly confronting the two leading proliferators and supporters of terrorism, Iran and North Korea," said Arizona Republican Sens. John McCain and Jon Kyl in a joint statement. 

"The Obama administration's policies, thus far, have failed to do that and this failure has sent exactly the wrong message to other would be proliferators and supporters of terrorism," they said.

The White House nuclear strategy review released Tuesday concluded the Obama administration will narrow the circumstances in which the U.S. might launch a nuclear strike, will forego the development of new nuclear warheads and will seek even deeper reductions in American and Russian arsenals.

In presenting the results of the administration's policy review, Gates said a central aim was to reduce the role of nuclear weapons in U.S. defense strategy.

That will be include removing some of the intentional ambiguity about the circumstances under which the United States would launch a nuclear strike, Gates told reporters at the Pentagon.

"If a non-nuclear weapons state is in compliance with the Non-Proliferation Treaty and its obligations, the U.S. pledges not to use or threaten to use nuclear weapons against it," Gates said. 

If, however, such a state were to use chemical or biological weapons against the United States or its allies, "it would face the prospect of a devastating conventional," or non-nuclear, military response.

But former CIA spokeswoman and Republican strategist Jennifer Millerwise-Dyck told Fox News that nuclear weapons have been an important deterrent tool used for decades both Democratic and Republican administrations," and shouldn't be dismissed.  

"If you look at history, and the time after the Cold War, it was a great deterrent for the Soviet Union when it came to preventing them from invading eastern European countries, for example. What you see here is part of what is rather disturbing pattern where the Obama administration continues to take away capabilities that the U.S. needs in its arsenal," she said.

Supporters say Obama's review, which does not require congressional approval, does not mean nuclear weapons are being removed from the playbook never to return. But Obama's current push is designed to strengthen international support for strengthened nonproliferation efforts.

"Given Al Qaeda's continued quest for nuclear weapons, Iran's ongoing nuclear efforts and North Korea's proliferation, this focus is appropriate and, indeed, an essential change from previous" policy, Gates said.

Backers also say the strategy is not intended for nations that violate the Nuclear Non-Proliferation Treaty like Iran, which is a signatory but is believed to be in defiance of the pact. 

Iran says its uranium enrichment facilities are for peaceful purposes and therefore it is not in violation of the NPT even though it has refused International Atomic Energy Agency inspections required by the pact.

The president's proposed policy was mocked outright Wednesday by Iranian President Mahmoud Ahmadinejad.

"American materialist politicians, whenever they are beaten by logic, immediately resort to their weapons like cowboys," Ahmadinejad said in a speech before a crowd of several thousand in northwestern Iran. "Mr. Obama, you are a newcomer. Wait until your sweat dries and get some experience."

Tuesday's announcement was well received by U.N. Secretary-General Ban Ki Moon.

"The secretary-general looks forward to the leadership of the United States in cooperation with other nuclear-weapon states, on further reducing and eliminating the role of nuclear weapons in
security policies, which would contribute to nuclear disarmament and non-proliferation," said a spokesman for Ban.

Rep. Buck McKeon of California, the top Republican on the House Armed Services Committee, said the policy change could carry "clear consequences" for security and he was concerned by "some of the language and perceived signals imbedded" in the policy. However, McKeon added that he is pleased the administration is keeping some of the existing deterrence framework and has "acknowledged that the conditions for a 'nuclear-free' world do not exist at this time."

But Millerwise-Dyck said biochemical attacks and other non-traditional threats go back to the the Clinton administration and nuclear deterrence was seen then as "a very important part of our way of protecting ourself." 

Now, she said, "We have taken that off the table and I don't know what we've gotten out of it. It's not as if Iran is going to stop pursuing or something because we said, 'Don't worry, we won't attack a nation if they're not part of the club.'"

Frank Gaffney, a Reagan administration Defense Department official and president of the Center for Security Policy, told Fox News that the new policy is "arguably the latest evidence of the radicalism of the Obama administration."

"I think the fact that you've got a number of a military officers and secretaries of defense dressing this up doesn't change the fact that the president of the United States is embarked upon a truly radical and I think frankly hare-brained idea that we're going to somehow persuade everyone else in the world, including all the nuclear weapon states to give up their nuclear weapons if we progress inexorably toward the obsolescence and ultimately irrelevance of ours."

Gaffney added that Obama's rhetoric on devaluing, cutting and not modernizing U.S. nuclear weapons "ultimately is going to reduce the deterrent that we have to something that we're going to have to pray people still think might work and therefore still be deterred by."

The Associated Press contributed to this report.