WASHINGTON — ONE night in November 1993, a Russian naval officer walked out of a shipyard in Murmansk carrying 10 pounds of highly enriched uranium. Intended for use as fuel in Navy nuclear reactors, the valuable loot had been poorly guarded - just like the officer's brother, a shipyard worker, had said. It was stashed in a garage and awaiting a buyer before police caught up with the thief.
As this crime shows, the threat of nuclear smuggling from the atomic arsenal of the former Soviet Union is much more than a Steven Seagal movie plot. Since the fall of 1992 there have been five serious thefts of weapon-usable fissile material from ex-Soviet stocks, according to a US presidential panel studying the subject.
Some experts say the amounts stolen in some of these cases were actually large enough to produce an atomic bomb. And witnesses who appeared at two days of congressional hearings on ''loose nukes'' this week agreed on one point: Neither Washington nor Moscow is doing enough to head off this danger.
''The actions of the US government and of the Russian government are not remotely proportionate to the problem and the challenge'' of maintaining ex-Soviet nuclear control, said Graham Allison, former assistant secretary of defense for policy plans.
A main cause of post-cold-war nuclear danger is the change now sweeping through society in Russia and other former Soviet republics, witnesses told the Senate Foreign Relations Committee hearings.
For one thing, the Russian military is facing a crisis of purpose: pay, morale, and discipline are plummeting across the board. Last week, a sub crew refused to put to sea because they hadn't been paid for at least two months, said Paul Goble, a former State Department special adviser on Soviet problems.
Civilian nuclear workers face similar straits. Nuclear scientists now make less than factory workers, in some instances. The Russian nuclear production ministry MINATOM ''has told personnel at their facilities that they can no longer rely solely on government funds to support them,'' said CIA nuclear analyst David Osias in a rare public appearance.
In this environment, accountability for Russia's vast stocks of nuclear-usable material has become a major problem. Over the years, tons of plutonium and highly enriched uranium have been distributed to various military bases, civilian institutes, and centers for nuclear science. Eighty percent of these facilities have no electronic monitors that can detect fissile material leaving the premises, according to Russian press reports. Civilian labs have particularly poor security, and may have been the source of almost a pound of plutonium seized by German police in Munich last August.
And willing buyers for Russian nuclear material certainly exist. Some countries opposed to the US are trying to acquire atomic weapons, pointed out the CIA's Osias, ''Iran and Iraq being two of our greatest concerns.''
The known instances of attempted nuclear theft thus should come as no surprise. The case which gives experts the greatest concern was uncovered in Vilnius, Lithuania, in 1993, when authorities seized four tons of beryllium mixed with highly enriched uranium stolen from a Russian nuclear-research institute.
The amount of usable bomb material that could have been extracted from this haul remains in dispute. But the case had all the elements of the experts' worst case ''loose nuke'' scenario. A senior regional Russian government official was involved in the diversion, as well as figures linked to the former KGB, and a known Middle Eastern arms merchant. The contraband material was mixed with legitimate scrap metal and scattered throughout 33 packing crates. All told, it showed the ease of diverting large amounts of fissile material by cloaking it in a normal commercial transaction.
''Much larger shipments of metal are routinely exported from Russia legally,'' said Thomas Cochran, director of nuclear programs at the National Resources Defense Council.
It takes only four pounds of plutonium to make a bomb, Cochran told the Senate Foreign Relations Committee. (US government officials say it would take substantially more, but Cochran claims they are bound by national security from revealing the true, lower figure.)
The centerpiece US effort to help Russia control its nuclear weapons and material is the so-called Nunn-Lugar program, which pays for such things as better security equipment. The Congressional hearings were called by this effort's co-sponsor, Sen. Richard Lugar (R) of Indiana, Foreign Relations Committee chairman and GOP presidential hopeful.
Indeed, the purpose of talking over this problem for two days seemed partly to build Congressional support for Nunn-Lugar's $371 million 1996 budget request. Even this amount of money isn't enough, said Sen. Lugar and the witnesses who paraded in front of him.
''To date, the US response to this new threat of nuclear leakage has not even begun to approximate US stakes in the matter,'' said Senator Lugar.