South Korean protesters with defaced photos of North Korean leader Kim Jong Il shout slogans during a rally Tuesday against North Korea’s nuclear test near the U.S. embassy in Seoul, South Korea. North Korea fired three short-range missiles off its western coast, a news report said Tuesday, a day after the country defied world powers and carried out an underground test of a nuclear bomb.

Washington ? A decade after its defeat on the Senate floor, the treaty to ban all atomic bomb tests has found new life in the age of Obama, and at a time of renewed nuclear defiance by North Korea.

Monday’s bomb test by the Pyongyang government “underlines the urgency of the entry into force of the (treaty) and the necessity of putting an end to all nuclear explosions for all time,” said the pact’s chief booster, Tibor Toth, who heads the U.N.-affiliated Comprehensive Test Ban Treaty Organization.

In the coming months in Washington — and in other key capitals — leaders will make cold strategic calculations as they weigh military balances and the future role of doomsday weapons in deciding whether to ratify the CTBT. Passage in the Senate this time around may set dominoes toppling from Beijing to New Delhi and beyond, Toth said.

“The U.S. example will be defining,” he told The Associated Press in an interview at his Vienna headquarters.

The treaty

Negotiated in the 1990s, the treaty specified 44 nuclear-capable states — from Algeria to Vietnam — that must give full formal approval before it can take effect, putting the power of international law and the U.N. Security Council behind the ban. All but nine of those have ratified, along with the governing bodies of 113 other nations.

Besides the U.S., the holdouts among the 44 are China, Egypt, India, Indonesia, Iran, Israel, North Korea and Pakistan.

Although earlier treaties outlawed all but underground nuclear blasts under 150 kilotons — equivalent to 150,000 tons of TNT — this one would impose a blanket ban on any test anywhere, with compliance overseen by Toth’s agency.

It would end an era in which eight nations exploded 2,054 nuclear bombs in the air, under water and below ground, from the mushroom cloud of July 16, 1945, at Alamogordo, N.M., and the U.S. bombings of Hiroshima and Nagasaki, to North Korea’s underground blast on Monday, its second test, estimated at a yield of a few kilotons.

The tests helped weapon designers build ever more compact, durable and finely tuned bombs. Ending testing would put a cap on developing new weapons, halting proliferation to more states and giving nuclear-armed states more confidence to negotiate deep reductions, treaty proponents say.

‘The climate is different’

President Barack Obama endorsed this view in an agenda-setting speech in Prague, Czech Republic, on April 5, when he said he would “aggressively” pursue Senate ratification. A vote may come next year, after a lobbying campaign to win the required two-thirds Senate majority.

Republicans controlled the upper house in 1999 when the pact was rejected 51-48 on a largely party-line vote. The debate focused on whether the treaty’s monitoring system could detect clandestine nuclear blasts, and whether the U.S. arsenal would remain safe and reliable without tests.

Much has changed since then: The monitoring system has grown into a $1 billion, high-tech worldwide network, and the U.S. weapons stockpile has been certified reliable annually since the 1990s, as the U.S. and four other original nuclear powers — Russia, Britain, France and China — have observed testing moratoriums.

The Senate has changed as well, with a 60-vote Democratic majority likely, just seven short of two-thirds. Meanwhile, some influential Republican voices have shifted to support the treaty, including former secretaries of state Henry A. Kissinger and George P. Shultz. Sen. John McCain, R-Ariz., said during his 2008 presidential campaign the treaty deserved “another look.”

“The climate is different and that’s important,” former Democratic Sen. Sam Nunn, a leading arms-control advocate, told the AP. “The fact the president has made this a top priority means it’s going to get a lot more attention from the American public than it did the last time.”

And more attention from the rest of the world.

“If the U.S. keeps its promise to push for ratification of the CTBT, it will serve as a catalyst for similar action by other states,” Indonesia’s U.N. ambassador, Marty Natalegawa, said May 5 at a disarmament conference in New York.

Domino effect

Toth said Indonesia, which has no nuclear weapons, is one holdout showing “positive signs” on ratification. Another is a big one: China.

“China supports early entry into force of the CTBT,” Beijing’s arms control chief, Cheng Jingye, told the same U.N. conference.

It has been clear since 1999 that China withheld ratification because the U.S. did. Toth said the Chinese now are “closely following developments in Washington” and assure him they are preparing to ratify.

If the U.S. Senate accedes, Obama pledges a diplomatic effort to bring other governments aboard. Nuclear-armed India is a likely target, since a recent U.S.-Indian civilian nuclear agreement gives Washington added leverage with New Delhi.

The Indians’ chief nuclear envoy, Shyam Saran, told the AP his country wants to see broad movement toward abolition of nuclear arms before committing to a test ban. Some analysts believe, however, that a CTBT ratification by China, the Asian rival whose bomb motivated India to build its own, might induce the Indian “domino” to follow suit.

And what about next-door Pakistan, with at least 40 nuclear warheads, to traditional enemy India’s 50 or more?

“Our response (on CTBT) depends very much on the position taken by India,” Zamir Akram, Pakistani ambassador to the Conference on Disarmament in Geneva, told the AP.

North Korean response

In the Middle East, nuclear-armed Israel is known to have backed off early ratification only because the U.S. did. Accession to this major nuclear agreement might help lift the global embargo on civilian nuclear trade with Israel. Egypt might then logically follow.

If Iran, accused of harboring plans for nuclear bombs, or North Korea, with rudimentary weapons, remained holdouts, they would face ever-growing isolation and international pressure to join.

Toth indicated he wouldn’t be surprised by a North Korean ratification, if Pyongyang sees all of the “P-5” — the original nuclear powers — behind the treaty and no longer demanding that North Korea accept restrictions that they don’t.

On the other hand, analysts say, a repeat failure to ratify in Washington could send dominoes tumbling in the other direction. China might feel a need to resume testing to perfect bombs for multiple-warhead missiles, to match U.S. capabilities. A testing chain reaction among nations might ensue.

“What the nuclear powers do, in fact, does affect the decisions of other countries,” veteran U.S. arms negotiator James Goodby told a nonproliferation conference in Washington last month. “And testing is perhaps the most visible of nuclear weapons activities.”