WASHINGTON » At the heart of President Barack Obama's new nuclear strategy lies a central gamble: that an aging, oversize, increasingly outmoded nuclear arsenal can be turned to the new purpose of adding leverage to the faltering effort to force Iran and North Korea to rethink the value of their nuclear programs.

The 50-page “;Nuclear Posture Review”; released yesterday acknowledged outright that “;the massive nuclear arsenal we inherited from the cold-war era”; is “;poorly suited to address the challenges posed by suicidal terrorist and unfriendly regimes seeking nuclear weapons.”;

Nonetheless, the new strategy aims to use the arsenal to do just that, despite considerable skepticism that any new doctrine or set of White House announcements is likely to change the calculus for North Korea or Iran.

Obama's new strategy makes just about every nonnuclear state immune from any threat of nuclear retaliation by the United States. But it carves out an exception for Iran and North Korea, labeled “;outliers”; rather than the Bush-era moniker of “;rogue states.”; The wording was chosen, Obama's senior advisers said, to suggest they have a path back to international respectability — and to de-targeting by the United States.

Secretary of Defense Robert M. Gates made the choice explicit. “;There is a message for Iran and North Korea here,”; he told reporters on Tuesday.

Nonnuclear states that abide by the Nuclear Nonproliferation Treaty would not be threatened with nuclear retaliation by the United States — even if they launched conventional, biological or cyber attacks. But, he added, “;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.”;

A number of analysts argued that, by publicly painting a target on Iran and North Korea, the administration could unwittingly bolster hard-liners in those countries, who have made the case that nuclear weapons are the only way to ensure their safety against American plotting.

The other side of that argument came from two senior Republican Party national security experts — Sens. John McCain and Jon Kyl of Arizona — who contended that the pressure was not direct enough.

“;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,”; they wrote. “;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.”;

To Obama and his aides, the “;outlier”; approach is all part of a broader strategy of adding to the pressure on both countries. Over the past year, they have aided the interception of North Korea's shipping. They have sought to develop new sanctions against the Iranian Revolutionary Guard Corps and to undermine its nuclear program with a program of covert action.

Robert S. Litwak, vice president for programs at the Woodrow Wilson International Center for Scholars, said that Obama had expanded an effort begun by President George W. Bush to globalize the effort to contain the nuclear aims of both nations.

Under Obama's strategy, he said, “;It is the United States and the world versus Iran, not just the United States versus Iran.”; (Bush's former aides note that during their time in office, they pushed through four United Nations Security Council resolutions against Tehran, though to little effect.)

The new strategy takes that effort one step further, warning both countries that the United States could still use its nuclear arsenal to counter any effort to sell or transfer the country's nuclear technology to terrorists.

“;The United States will continue to hold accountable any state, terrorist group or other nonstate actor that supports or enables terrorist efforts to obtain or use weapons of mass destruction,”; Gates said Tuesday, “;whether by facilitating, financing, or providing expertise or safe haven for such efforts.”;

The problem Obama faces is that the Bush administration used virtually identical language to warn North Korea soon after it conducted a nuclear test in 2006. The next year, however, North Korea was caught helping Syria build a nuclear reactor. Israel destroyed the site in a nighttime raid in 2007. But North Korea paid little price for what is widely regarded as its most audacious attempt at nuclear proliferation.

Obama, asked on Monday whether that episode harmed American credibility, said, “;I don't think countries around the world are interested in testing our credibility when it comes to these issues.”;

“;The message we're sending here,”; he said, was that countries that “;actively pursue a proliferation agenda”; would not be immune from any form of American retaliation, including nuclear.

The reality is more complex. If a backpack nuclear bomb went off in Times Square or on the Mall in Washington, the Pentagon and the Department of Energy would race to find the nuclear DNA of the weapon — so that the country that was the source of the material could be punished. But the science of “;nuclear attribution”; is still sketchy. And without certain attribution, it is hard to seriously threaten retaliation.

The nuclear review also details a larger set of tools to shape the behavior of Iran and North Korea. By reducing the size of America's own stockpiles, and assuring nonnuclear states inside the nonproliferation treaty that they are exempt from any nuclear attack, the administration hopes to bolster its credentials to close huge loopholes in the treaty that both North Korea and Iran have artfully exploited.

“;We think we now have (the) credibility Bush never did,”; one of Obama's aides said, “;to tighten the noose. But it will be a very, very slow process.”;