Proposed nuclear reductions point to concern about Russia's eroding military.(Knight Ridder Newspapers)

WASHINGTON _ President Bush's call Tuesday for an accelerated development of U.S. missile defenses in part reflects concern that Russia could mistakenly launch a nuclear attack on the United States.

The threat stems from deepening decay in the early-warning network of satellites and radar on which Moscow counts to detect an incoming U.S. nuclear attack and fire back before its own nuclear forces are obliterated.

Russian satellites are unable to monitor the 550 U.S. intercontinental missile silos for about 18 hours a day, while Russian radar cannot cover northern areas of the Atlantic and Pacific oceans where missile-armed U.S. submarines are always stationed, say experts inside and outside the U.S. government.

That's longer than those experts thought even a year ago.

Unable to accurately monitor U.S. activities, the Russian military could misread a non-threatening rocket launch or missile test as an attack, and then retaliate with a salvo of nuclear warheads kept on hair-trigger alert, these experts say.

"The value of an early warning system is not so much that it doesn't give false alarms, but lets you know that benign events are benign," said Geoffrey Forden, a researcher at the Massachusetts Institute of Technology, who tracks Russia's early warning system. He says Russia now has little ability to distinguish benign events from threatening ones.

Bush's effort to accelerate U.S. missile defense development programs is in part an attempt to enable the United States to neutralize an inadvertent or unauthorized Russian missile attack.