Pakistan will confront its reputation as a proliferator head-on this week when its prime minister addresses a global summit in Washington aimed at keeping nuclear weapons out of the hands of terrorists.

Arch-rival India and other critics could however undercut Pakistan by reminding the world of its nuclear smuggling, highlighting the Taliban insurgency and fanning fears of a Muslim country in chaos where militants could seize atomic material.

"India will demand restrictions imposed on Pakistan's nuclear programme," said Shahid-ur-Rehman, a Pakistani journalist and author of "Long Road to Chagai", a book on Pakistan's nuclear programme.

"Their main stress will be on securing Pakistan's nuclear assets by the world," he told newsmen.

"Pakistan's efforts will be to counter that and convince them that our National Command Authority, which oversees the country's strategic assets, is very effective and that our nuclear assets are safe and secure."

Pakistani Prime Minister Yusuf Raza Gilani will speak at the summit after meeting President Barack Obama on Sunday. There are no plans for Gilani and his Indian counterpart, Prime Minister Manmohan Singh, to meet, although the leaders of the nuclear-armed rivals may have a brief "encounter".

Obama called the Nuclear Security Summit to reach a common understanding on the threat posed by nuclear terrorism and an agreement on steps to secure all loose nuclear material within four years to stop it falling into the hands of groups such as al Qaeda.

U.S. Secretary of State Hillary Clinton says the April 12-13 gathering of 47 nations is possibly the largest assembly of world leaders in the United States since 1945.

Two countries not on the guest list are Iran and North Korea, both of which are locked in their own nuclear standoffs with the West. And both countries have allegedly benefited from the smuggling network of Abdul Qadeer Khan, the father of Pakistan's nuclear bomb and a national hero.

It is this history -- and Pakistan's uncertain future -- that has put the country's nuclear programme in the spotlight this week. Experts say Pakistan's arsenal and stockpile of weapons-grade material represent the area of greatest risk, because of huge internal security threats from the Taliban and al Qaeda.

"Because of Pakistan's so-called past, that there was proliferation from Pakistan and that Pakistani scientists had met Osama bin Laden ... there will be pressure on Pakistan," said Rehman, referring to reported meetings involving two retired Pakistani nuclear scientists before the Sept. 11 attacks.

"America and the West's biggest concern is that weapons of mass destruction should not fall into extremists' hands and, in this case, they seem to be tacitly pointing at Pakistan. India and the anti-Pakistani lobby have always tried to exploit that and they will try to do it again."

Pakistan dismisses that concern, calling it "speculative".

"I do not see any possibility, whatsoever, of Pakistani material, or nuclear technology falling into the wrong hands," a spokesman for the Foreign Ministry, Abdul Basit, told newsmen.

"India knows full well how secure Pakistan's strategic assets are."

Obama says he's confident in the security of Pakistan's arsenal, but India isn't so sure.

The neighbours have fought three wars since being carved out of colonial India in 1947 and engaged in several smaller conflicts, including one in 1999 that threatened to go nuclear.

Both nations conducted nuclear tests in 1998.

Currently, they have an agreement to share prior information about new missile tests they plan to carry out, as well as an agreement to share details about each other's nuclear facilities and their safety on a periodical basis.

But their armies often exchange fire across the border, and peace talks are held only intermittently.

"There is a lot of mistrust as India keeps on receiving reports of secret (nuclear) installations in Pakistan, and it believes that Islamabad is not sharing all its details," said Naresh Chandra, India's former envoy to Pakistan.

India is aware, however, of Pakistan's importance to U.S. and NATO forces in Afghanistan, so it doesn't expect much American intervention between the two on nuclear issues, Chandra added.

There is more at stake in Washington than nuclear one-upmanship between old enemies. Pakistan's economy has been hammered by energy shortfalls and high on its wish-list is a civilian nuclear deal with the United States like the one India received under President George W. Bush.

It has been repeatedly rebuffed by the United States -- although lately more gently -- and media reports in Pakistan suggested China may step up and help with civilian nuclear technology.

That would likely make India even more suspicious because of its own rivalry with China. The two fought a war in 1962.

Washington also would like Pakistan's help in curtailing Iran's nuclear programme, although there appears little chance of that.

According to the Stockholm International Peace Research Institute, India has between 60-70 warheads while Pakistan has about 60. Neither India nor Pakistan are party to the Treaty on the Non-Proliferation of Nuclear Weapons that Obama hopes to strengthen.