Islamabad, Pakistan ? A leading Pakistani nuclear scientist, barred by his government from talking to reporters, has made it known through his son that Osama bin Laden approached him before the 9-11 attacks for help in making nuclear weapons.

The al-Qaida leader was rebuffed, the son, Azim Mahmood, said in a recent interview with The Associated Press.

“Basically Osama asked my father, ‘How can a nuclear bomb be made, and can you help us make one?”‘ he said. “My father said, ‘No, and secondly you must understand it is not child’s play for you to build a nuclear bomb.”‘

The scientist, Sultan Bashiruddin Mahmood, is under a gag order from Pakistani intelligence officials, but his conversations with bin Laden in meetings in 2000 and as late as July 2001 were reconstructed for the Associated Press by his son.

The conversations as described by Azim Mahmood clearly show bin Laden was interested in developing nuclear weapons. They don’t, however, shed any light on whether the terrorist mastermind had taken even the first steps on that complex technological challenge.

The U.S. Embassy declined to discuss Mahmood’s story. American officials in Washington, D.C., also would not comment.

There has been previous evidence of al-Qaida’s interest in nuclear weapons.

Computers found by journalists and U.S. troops at a variety of facilities in Afghanistan indicated al-Qaida had sought to obtain and develop nuclear and other potent weapons. An AP reporter saw anthrax and other chemical concoctions at an al-Qaida laboratory outside Kabul.

During a New York trial two years ago stemming from bombings at two U.S. embassies in Africa, a former bin Laden aide testified he was ordered in 1993 to try to buy uranium on the black market for an effort to develop a nuclear weapon. Jamal Ahmed Al-Fadl said al-Qaida was prepared to spend $1.5 million, but he didn’t know whether a purchase was ever made.

‘Dirty bomb’ sought

In addition, U.S. officials have said captured al-Qaida lieutenant Abu Zubaydah told American interrogators the terrorist network was working on a “dirty bomb,” a conventional bomb that would scatter radioactive material. Such a radiological weapon would be far less deadly and damaging than a nuclear explosion.

Authorities also have said that Jose Padilla, the former Chicago gang member charged with plotting with al-Qaida, attended two meetings in Karachi, Pakistan, at which senior al-Qaida operatives discussed the possible use of a “dirty bomb.”

A United Nations report issued by experts monitoring al-Qaida movements warned that al-Qaida has the potential to obtain nuclear material and build “some kind of dirty bomb.”

“Our concern is you can actually get the stuff,” said Michael Chandler, the British expert who leads the monitoring group.

Nuclear ambitions

The conversations related by Azim Mahmood confirm bin Laden’s nuclear ambitions. But they also offer a glimpse at the nexus of science and conservative Islam at a high level in Pakistan, one of the world’s newest nuclear powers along with neighboring India, whose own leaders follow a Hindu fundamentalist philosophy.

The elder Mahmood, who has been questioned by the FBI and is under close Pakistani surveillance, is a deeply conservative Muslim who espouses the same puritanical brand of Islam as Afghanistan’s former Taliban rulers.

Enraged over Pakistan’s plans in 1998 to sign the Comprehensive Test Ban Treaty, he resigned from the Pakistan Atomic Energy Commission and devoted his time to his charity, the Holy Quran Research Foundation.

Last December, President Bush labeled the charity a terrorist group and Mahmood a terrorist. His assets and those of his charity were frozen.

“Even my father’s pension is blocked. At the moment he has nothing,” said Azim Mahmood, a physician in his 30s who also adheres to a strict Islam.

For years, Pakistani peace activists and liberal academics have fretted about Islamic hard-liners in Pakistan’s nuclear organization.

“We have always expressed our fear that a large number of people in the nuclear establishment would be ideologically motivated to share Pakistan’s nuclear weapons technology,” said A.H. Nayyar, a nuclear physicist and research fellow at the Sustainable Development Policy Institute, an independent Pakistani group.