Just days after the Pentagon's latest failure to shoot down one missile with another, key senators warned that the proposed national missile defense (NMD) system was not yet technologically feasible, and that opposition from Russia and China suggested it could actually harm national security.

"This system is not ready for prime time. No president, this one or the next one, unless things change drastically, should in fact deploy this system," said Senator Joseph Biden, the top Democrat on the Senate Foreign Relations Committee.

"There's no way that we can say that this system will be operationally effective, given the failure of this last test, given the technological complexity of this," said Carl Levin, the top Democrat on the Senate Armed Services Committee.

Senate Democratic Minority Leader Tom Daschle told reporters he would urge Clinton, set to make a decision later this year on the 60-billion-dollar program, to let the next administration decide whether to push forward with NMD.

The comments came after the Senate voted 52-48 to shoot down a proposal that would have toughened testing of the missile shield, pitting it against countermeasures that many scientists say would easily render it impotent, including boosting the number of warheads or launching decoys.

"Now the Senate is on record as saying it doesn't matter whether it works or not, we're going to build it any way," Daschle deplored.

The vote reflected the staunch support for the program, which backers say is critical to thwarting attacks by nations like North Korea, Iran or Iraq. Clinton's decision would start the ball rolling towards having an operational NMD by 2005.

Critics -- pointing to recent testing failures -- say NMD is not currently feasible and could destabilize US ties with Russia and China, which say the plan violates the 1972 Anti-Ballistic Missile (ABM) treaty.

"We don't have sufficient information about its technological feasibility, we really don't know what its impact is going to be on ABM, we really don't know its effect on overall national security," said Daschle.

If Clinton does not give the go ahead this year to start construction on the first piece of the system -- a high frequency radar on Shemya island in Alaska -- the Pentagon will be unable to deploy the system by 2005, Pentagon officials said.

Technological concerns include a group of scientists' assertion that any nation technologically able to launch a missile could defeat the missile shield by multiplying the number of warheads or sending up decoys to overwhelm the system.

Of three attempted interceptions, two have failed, falling short of the Pentagon's own minimum criteria of scoring two intercepts before declaring the system ready for deployment in 2005. That is when US intelligence services estimate that North Korea is likely to have long-range missiles capable of striking the United States.

Russian Foreign Minister Igor Ivanov joined other G8 representatives at the two-day meeting here in questioning the fall-out from any deployment of a US national missile defence (NMD) program.

US Deputy Secretary of State Strobe Talbott had to fend off concerns that the unproven system threatened to undermine the anti-ballistic missile (ABM) treaty.

"With respect to NMD, there was discussion of that in the context of a broader discussion on arms control and non proliferation," Talbott told a joint news conference here.

Just five days ago, the United States admitted an interceptor rocket had failed to shoot down an incoming dummy warhead during a 100-million-dollar test of its prototype NMD system.

The botched test was an acute embarrassment to the Pentagon and US President Bill Clinton, who is due to take a decision on whether to deploy the 60-billion-dollar system by the year's end.

But Talbott said the test was only part of a series, and would not determine the system's fate.

Clinton would also take into account the effect of NMD deployment on missile reduction agreements and global stability when deciding on implementation, Talbott said.

"I very much valued the opportunity to hear directly from the foreign ministers of a number of our key allies who have their own concerns and perspectives," he said.

Russia's Ivanov had expressed Moscow's worries in a lunch with the US diplomat on Wednesday, Talbott noted.

Those concerns would be raised again, he said, when Clinton met with Russian President Vladimir Putin at a July 21-23 G8 leaders' summit in the southern Japanese island of Okinawa.

The two leaders might find common ground on the threat posed by the proliferation of ballistic missiles, a key factor cited by the United States in favour of NMD, Talbott said.

Their negotiations would try bring "Russia and the United states even closer together in dealing with new threats that have arisen as a result of the proliferation of ballistic missile technology."

The NMD program has been driven by US intelligence estimates that North Korea is likely to have long-range missiles capable of striking the United States by 2005.

Paris had expressed "questions over the nature of the threat and our concern regarding the strategic consequences of any decision that would be taken by the US president," French Foreign Minister Hubert Vedrine told AFP.

A statement issued by the G8 ministers after two days of talks in the southern Japanese city of Miyazaki stressed support for ABM treaty and the Russia-US START II treaty on reducing nuclear weapons.

It looked forward to "the conclusion of START II as soon as possible while preserving and strengthening the ABM treaty as a cornerstone of strategic stability and as a basis for further reductions of strategic offensive weapons, in accordance with its provisions."