A new U.S. intelligence report says Russia's nuclear material and power plants are vulnerable to theft and terrorism, despite U.S.-aided efforts to increase security.

The unclassified report to Congress was prepared by the National Intelligence Council, an analytical group that reports to CIA Director George Tenet.

Russia has increased security at its nuclear facilities, including its power plants, since Sept. 11, the report says. Russian officials, including President Vladimir Putin, have embarked on a campaign to assure the public that the country's nuclear materials are safe from terrorists.

"Even with increased security measures, however, such plants almost certainly will remain vulnerable to a well-planned and executed terrorist attack," the report says.

Russia's weapons-grade plutonium and uranium also remain vulnerable to theft, the report says. Some of these materials are housed at Ministry of Atomic Energy facilities and other Russian institutes.

These facilities "typically receive low funding, lack trained security personnel, and do not have sufficient equipment for securely storing such material," the report says.

The report cites several instances in which a few kilograms of enriched uranium have been reported stolen, as well as a reported 1998 theft of "quite sufficient material to produce an atomic bomb," according to a senior Russian official. The U.S. intelligence report, however, says that theft has not been independently confirmed.

Authorities have reported fewer attempts since then to steal weapons-grade material, and fewer seizures of stolen items. It's unclear if that's good news or bad: Either increased security is discouraging theft, or the thieves are getting better at avoiding security.

"We assess that undetected smuggling has occurred, although we do not know the extent," the report says.

The report singles out a widely reported February 2001 incident in which U.S. investigators found a fence gate to a weapons material storage site left open and unguarded during the day.

"Convenience and pressure to produce also can contribute to lapses in security," the report says.

Russia's actual nuclear weapons numbering about 5,000 strategic warheads and an unspecified number of tactical devices are reasonably secure, the report says.

"An unauthorized launch or accidental use of a Russian nuclear weapon is highly unlikely as long as current technical and procedural safeguards ... remain in place," the report says.

The primary threat is from an insider who tries to use or steal a weapon, especially if central political authority in Russia breaks down, the report says.

Some officials said security was already high at facilities due to the threat of attacks by Chechen separatists. The report quotes the head of the Russian nuclear weapons storage program, Gen. Col. Igor Valynkin, saying authorities had twice stopped terrorist efforts to survey storage sites.

One goal of Usama bin Laden's Al Qaeda organization has been to obtain nuclear weapons, either by buying, stealing or making them, U.S. officials say. He is not believed to have succeeded.

The United States has several cooperative programs with the Russians aimed at increasing nuclear security.