The United States and Russia could take thousands of strategic nuclear warheads off hair-trigger alert by introducing an early warning system of sensors that monitor each other's land-based intercontinental missiles, according to former senator Sam Nunn (D-Ga.), who once was chairman of the Armed Services Committee.

Nunn said President Bush and Russian President Vladimir Putin, who are to meet in St. Petersburg next month, should "order their defense and military leaders . . . to devise changes in the operational status of their nuclear forces."

Nunn spoke to reporters yesterday as he introduced a study by the Rand Corp. on a phased approach for improving nuclear safety between the two countries.

The monitoring system, being developed by Sandia National Laboratories in New Mexico and Kurchartov Institute in Moscow, is being used on a test basis to monitor stored nuclear materials taken from dismantled weapons. The sensors transmit data to a central monitoring center in one country, which transmits the information by satellite to the other country.

Kurchartov scientists have proposed adopting the system for early warning purposes, according to the Rand study, which was sponsored by the Nuclear Threat Initiative, a think tank where Nunn is co-chairman.

Despite the improved relations between Moscow and Washington and a treaty a year ago to reduce strategic warheads to below 2,000 each, Nunn said each country keeps about 4,000 warheads on alert. "Twelve years after the end of the Cold War, what requires us to continue to live with the risk of an accidental or unauthorized nuclear launch?" he said.

Nunn said that there has been no change, because "as long as Russia can launch nuclear ballistic missiles on short notice against the U.S., the U.S. must maintain a similar capability against Russia."

The situation has been made worse by the growing vulnerability of Russian forces and increased accuracy of U.S. weapons, according to Rand. The study notes that Russian early warning space satellites, which once watched for launches from U.S. ICBM silos 24 hours a day, have declined to only seven hours a day. Russia has not launched an early warning satellite since 1998; a fire in the satellite control center in May 2001 further degraded the system, Rand said.

Russian ground-based early warning radar systems have developed significant gaps, because two second-generation radars were never built and the one being constructed at Krasnoyarsk was torn down as a violation of the now discarded Anti-Ballistic Missile treaty. As a result, the United States could launch nuclear missiles from a Trident submarine through a known coverage gap, and the launch could not be detected until the warheads exploded less than 10 minutes later in Russia, Nunn said.

In a May 2000 campaign speech, Bush said the United States "should remove as many weapons as possible from high-alert, hair-trigger status," Nunn said, adding, "Bush had it right in his statement three years ago."