Defence officials in the United States say that a one-day conference on nuclear weapons is taking place at the Strategic Air Command headquarters in Nebraska.
Arms control groups say the conference is to discuss whether to build a new generation of nuclear bombs, known as "mini-nukes", capable of destroying underground bunkers.
The US says it will not talk to Russia about resuming nuclear testing
President Bush's rival in the 2000 elections, Al Gore, has been speaking against further nuclear weapons development.
The meeting in Nebraska is taking place behind closed doors and the group of demonstrators who have turned up there are being kept well away.
A leaked Pentagon agenda indicates the defence officials and military scientists are discussing the viability of what are being called mini-nukes.
These would form a new generation of low-yield nuclear weapons which can be designed to bore deep underground before exploding, destroying hardened bunkers that might contain weapons of mass destruction.
Tests 'not planned'
The programme was criticised on Thursday by former Vice-President Al Gore in his first foreign policy speech in nearly a year.
"This administration wants to embark on a brand new programme to build a new generation of small nuclear bombs to bust bunkers under the ground.
"In my opinion, this would be true madness."
The Bush administration has rejected criticism that its nuclear weapons development studies are ill-timed, just as the US is seeking to stifle proliferation in Iran and North Korea.
Secretary of State Colin Powell, speaking in Washington, denied speculation that President Bush was planning to bring up the issue of resuming nuclear weapons testing when he next meets President Putin of Russia in September.
"The president has no intention of testing nuclear weapons. We have no need to and we have been consistent for some time on that issue," he said.
"We can't rule out forever... we have no plans to test, so I don't expect that to be a subject of discussion."
Whatever the reassurances, much of the groundwork is already laid for the development of mini-nukes.
Congress has already approved potential funding for bunker-busting bombs whose abilities would fit well with President Bush's preference for a pre-emptive strike capability.