CALGARY - Major powers were working through Wednesday night to finalize a $20 billion project to decommission weapons of mass destruction in the former Soviet Union, a key part of global efforts to deny militant groups access to nuclear arms.

Officials attending the summit of the Group of Eight industrialized countries said delegates were working on final details of the plan, which could offer $10 billion of U.S. funds and $10 billion from G8 partners over a decade.

"There seems to be an agreement that something close to $20 billion will be needed over the next 10 years," said an aide to Canadian Prime Minister Jean Chretien, who is chairing the summit of leaders from Britain, Canada, France, Germany, Italy, Japan, Russia and the United States.

But Chretien failed to win G8 approval at a dinner on Wednesday night for a deal he had hammered out with Russian President Vladimir Putin, and the G8 leaders' deputies were asked to pursue their talks overnight.

Italian Prime Minister Silvio Berlusconi had earlier said that the deal was done.

"The question of arsenals that could fall into the hands of evil-minded states interests all mankind and the decision (on the fund) was agreed by everyone almost without debate," he told a news conference on the first day of the summit.

Washington, which has already committed around $1 billion next year under existing programs to help Russia destroy the vast former Soviet nuclear stockpiles, has promoted the new program in the wake of the Sept. 11 attacks.

Diplomats say Western military chiefs are worried that leaky security at Russian atomic sites makes then vulnerable to al Qaeda and other militant organizations.

Berlusconi said Putin was delighted with the deal.

But Putin's chief foreign policy adviser Sergei Prikhodko said only that work was continuing.

"Some sort of results will be be achieved. Based on these results, we will consult further with our partners," he told a late-night news conference.

Berlusconi said Germany had promised to sink 1.5 billion euros into the fund, while the European Union would provide a further one billion euros. He said Italy would also contribute but did not specify how much cash it would hand over.

Japanese Prime Minister Junichiro Koizumi pledged his country would spend $200 million for now, a Japanese official said. Koizumi noted that Russia was mainly responsible for a delay in the program, and said Japan would make its contribution on the condition that Russia proceeded.

Chretien had earlier thrown out the possibility of Canada contributing $1 billion -- if all the others outside the United States did the same they would be close to $10 billion.

The Chretien aide said the disagreement appeared not to be on money but on nailing down obligations for Russia and the donors.

The plan should help Moscow deal with the 30,000 nuclear weapons and the highly enriched uranium and plutonium stocks it inherited when the Soviet Union broke apart in 1991.

Last year, a bipartisan U.S. task force said the need to secure Russian nuclear weapons, materials and scientific knowledge was "the most urgent unmet national security threat to the United States."

Experts say the G8 plan might focus on decommissioning some older Soviet-era nuclear power stations as well as constructing a mixed-oxide plant which would turn weapons-grade plutonium into fuel suitable for use in civilian reactors.