WASHINGTON - A GROUP committed to eliminating nuclear weapons presented on Monday a four-step plan to achieve that goal by 2030, while acknowledging that Iran could be a 'show stopper'.

The plan by the nonpartisan Global Zero Commission specifies that the United States and Russia, the world's largest nuclear powers, agree to reduce first to 1,000 warheads each, then to 500 each by 2021.

The United States is believed to have about 2,200 active strategic nuclear warheads and Russia about 2,800. Each has thousands more in reserve as well as large numbers of non-strategic, or tactical, nuclear arms.

During the second phase of cuts to 500, all other nuclear weapons countries would have to agree to freeze and then reduce their warhead totals. Those other countries are China, Britain, France, India, Pakistan and Israel but not North Korea, which has conducted nuclear tests but may not have a useable weapon.

In a third phase, from 2019 to 2023, a 'global zero accord' would be negotiated to include a schedule for the phased, verified reduction of all nuclear arsenals to zero total warheads. In the last period, from 2024 to 2030, the reductions would be completed and a verification system would remain in place.

The Global Zero Commission includes former and current senior officials from all existing nuclear powers. Among them: Russian lawmaker Mikhail Margelov, retired Chinese Major General Guangqian Peng and former US Republican Senator Chuck Hagel.

The plan's public unveiling was timed for the July 6-8 summit meeting between President Barack Obama and Russian President Dmitry Medvedev. In April the two leaders endorsed the idea of a nuclear free world, but neither country has proposed a way of achieving that goal, which many consider to be unrealistic.

The United States and Russia hold at least 90 per cent of the world's nuclear weapons. Global Zero Commission member Richard Burt, a former chief US negotiator for strategic nuclear arms reduction talks with the former Soviet Union, said the key to getting Washington and Moscow to reduce their warhead totals to 500 as an intermediate step is having other nuclear powers agree to freeze their arsenals and then join the United States and Russia in going the final step to zero by 2030.

An even stickier problem is Iran. Under the Global Zero Commission's plan, the Iranians would become an issue in the third phase, in the 2019 to 2023 period, when a global zero accord would be negotiated.

That is because the plan requires that all 'nuclear capable' countries - defined as those with nuclear power programs, civilian or otherwise - sign and ratify the accord in order for it to take effect. -- AP