The administration of US President Barack Obama is nearing the completion of a much-anticipated policy that could restrict the role of the nation's nuclear arsenal while strengthening the weapons-research infrastructure at the Department of Energy laboratories.

Initially scheduled for release late last year, and then again for 1 March, the Nuclear Posture Review will lay out the administration's justifications and strategy for maintaining a nuclear arsenal. It will also be the president's first opportunity to make good on his promise, made in Prague last April, to take "concrete steps" towards nuclear disarmament and to reduce the role of nuclear weapons in the US security strategy. The policy is likely to affirm the Obama administration's decision not to pursue new weapon designs, although many expect there to be wiggle room for scientists at the weapons labs to modify existing systems in the name of safety and security.

Officials are still debating how to frame the US nuclear strategy in the review, which is now expected sometime in the coming weeks. Some politicians and non-proliferation advocates have urged the president to promise that nuclear weapons will be used only to deter a nuclear attack, whereas others advocate a less restrictive phrasing.

"I personally expect to be disappointed," says Matthew Bunn, a nuclear expert at Harvard University in Cambridge, Massachusetts. "I think it will have some positive-sounding language, but I think the overall changes will be modest."

The document will help to guide work throughout the energy department, including at the primary weapons laboratories, Los Alamos National Laboratory in New Mexico and Lawrence Livermore National Laboratory in California, as the administration works on a new treaty with Russia that could see the weapons stockpile reduced. An expanded role for the labs was already clear from the administration's proposed fiscal budget for 2011, released last month.

In the budget, the National Nuclear Security Administration, based in Washington DC, which manages the weapons programme and non-proliferation activities within the Department of Energy, would receive a 13.4% increase to US$11.2 billion, including more than $7 billion to manage the nuclear stockpile. Of that, $1.6 billion would go towards science, technology and engineering programmes, which include advanced computer simulations, research into the ageing of nuclear materials, and fusion experiments at the Livermore lab's National Ignition Facilty. The goal is to ensure that ageing, untested weapons would work as designed.