"We are looking to find out more details about whether this represents anything new or is just what he said to (President Bill Clinton) over the weekend," said White House spokesman PJ Crowley Tuesday.

The spokesman said that when Clinton and Putin met in Moscow, they promised "to continue to discuss these issues."

The proposal, made by Putin during a visit with the Italian prime minister on Monday, comes as Washington and Moscow are discussing a US proposal to deploy a National Missile Defense system to protect it from "rogue states."

The project would require changes to the 1972 Anti-Ballistic Missile (ABM) treaty, a move Russia opposes.

Putin's proposal is "clearly an effort to propose an alternative to Clinton's plans," according to Joseph Cirincione, defense specialist at the Carnegie Endowment for International Peace, a Washington think-tank.

But Washington is unlikely to take it seriously, due to "strong pressure" from a US defense industry that won't want Russian companies to share in the financial benefits of building a missile shield, Cirincione said.

US Defense Secretary William Cohen had late Monday called Putin's proposal "a step forward."

"It's certainly a step forward to say there is a missile threat, which the president of Russia now recognizes," said Cohen of Putin's comments.

During a visit to Rome Monday, Putin called on the European Union and NATO to join forces with Moscow and set up a joint anti-missile shield.

Putin had said at a news conference such a move would "avoid creating problems linked to an imbalance in the equilibrium of forces."

He said it would also "ensure 100 percent the security of all European countries, with the obvious involvement of our American partners."

The Russian leader and US President Bill Clinton failed during a weekend summit in Moscow to agree on US plans for an anti-missile shield.