The landmark nuclear pact the United States signs with Russia Thursday will significantly boost President Barack Obama's moral hand in pursuing non-proliferation -- a key foreign policy goal.

Analysts said the treaty, one of the last symbolic remnants of the Cold War era, will also enhance Obama's long-term goal of eradicating nuclear weapons entirely, a target even he admits is unlikely to be realized in his lifetime.

More immediately, the replacement for the Strategic Arms Reduction Treaty (START) will lend credibility to Obama's nuclear security summit of world leaders on April 12 and 13.

Analysts said the treaty will reflect an emerging geopolitical truth -- that the protective shield of a nuclear arsenal, while not yet obsolete, is a remnant of an earlier bipolar superpower era.

Thousands of nuclear warheads, ballistic missiles and the power to wreak destruction on an enemy could not prevent the worst-ever attack on US soil -- not by a hostile nation state but by Al-Qaeda on September 11, 2001.

Obama will join Russian President Dmitry Medvedev to sign the successor treaty to the 1991 START deal that expired last year, in Prague -- the venue of a soaring speech by the US president last year on the need to tackle proliferation.

Their meeting and Obama's nuclear summit occur at a critical moment, as momentum gathers behind a US-led international effort to impose tougher sanctions on Iran over its nuclear program.

The new nuclear pact limits each side to 1,550 deployed warheads, about 30 percent lower than a previous upper warhead limit set in 2002.

It also caps the numbers of deployed intercontinental ballistic missiles and submarine-launched missiles.

Andrew Kuchins of the Center for Strategic and International Studies said the deal was an important step ahead of the nuclear summit in Washington and a nuclear non-proliferation treaty review conference in New York in May.

"They absolutely had to have this done," he said, though adding that the new treaty was far from a "magic key" to prod nuclear aspirant nations to reconsider atomic arsenals as a guarantor of their own security.

Without the treaty, Obama's long-term nuclear security goals "would have suffered a great setback," Kuchins said.

For Obama, the deal also offers political cover, providing a dividend for his decision to "reset" US relations with its former Cold War foe.

"The most obvious benefit from an American standpoint is that it certainly signifies a better relationship with Russia," said Doug Bandow, senior fellow at the CATO Institute think-tank.

He said the deal "does suggest that the Russian government is willing to deal with Washington on a more positive (framework) than it was with the Bush administration near the end of its term."

The new START pact also burnishes Obama's credentials as a statesman, offers a needed foreign policy success and may dampen criticism that his diplomacy is strong on rhetoric but short on achievements.

"With this agreement, the United States and Russia -- the two largest nuclear powers in the world -- also send a clear signal that we intend to lead," said Obama in announcing the treaty on March 26.

In a strategic sense, the arms deal reflects a strategic shift early in the 21st century away from the "balance of terror" rationale that prevailed between the United States and the Soviet Union.

"There's no question that the role of nuclear weapons in US security policy is diminishing slowly over time," said Kuchins.

The Obama administration will make its next foray into arms policy with the expected release of its nuclear posture review (NPR) in the coming days.

A White House official said last month that the document would "point to a greater role for conventional weapons in deterrence."

Still, Obama's aspirations herald a tricky political dilemma, at a time when other nations, including a rising China and North Korea, are increasing their arsenals, though their stocks are currently dwarfed by the US stockpile.

"If you want a degree of security in your country, you have to recognize that China is building up its arsenal, there are other countries out there, how low do you want to go?" said Bandow.

"That's going to be a challenge to this president."