MOSCOW, SEPT. 27 -- The Soviet armed forces chief of staff said today that the Kremlin has quietly withdrawn nuclear warheads from potential ethnic trouble spots around the country.

Gen. Mikhail Moiseyev said in an interview that the Soviet leadership recognizes that it has an obligation "before mankind" to ensure complete security over nuclear weapons. He added that "in those areas where the situation doesn't fully correspond to the concept of national security, the warheads have been put in a more secure place."

Moiseyev's comments marked the first authoritative Soviet confirmation of Western reports that the Kremlin has taken additional measures to ensure the safety of the world's largest stockpile of nuclear weapons. Western defense attaches here say they have received similar reassurances in private from their Soviet counterparts in recent months.

American concern for the security of Soviet nuclear weapons provides a vivid illustration of the changing relationship between Washington and Moscow as the Cold War winds down. The U.S. image of an aggressive but essentially stable Soviet Union is giving way to a new perception of an outwardly benign but internally unstable multinational state crammed full of weapons of mass destruction.

U.S. officials who once tried to calculate the chances of a deliberate Soviet nuclear strike against the United States are now more preoccupied with the specter of Soviet nuclear weapons falling into the wrong hands. Kremlin leaders, in turn, have begun to play on the new American fears, hinting that Washington would be well-advised to provide economic assistance to the Soviet Union to prevent economic collapse and political chaos.

Moiseyev, who was speaking on the eve of his departure for a tour of the United States, refused to specify precisely which areas of the Soviet Union he had in mind or when the warheads were removed. But Western defense attaches here believe that the regions affected include Central Asia, the southern Transcaucasus region and the Baltic republics, all of which have been the scene of serious nationalist upheavals over the past two years.

Asked to confirm the information of the Western attaches about removal of weapons, Moiseyev replied: "Where it was necessary for me to do it, it has been done reliably. I share your concern. . . . All the necessary measures have been taken. Chernobyl was enough. We have no right before humanity to be the origin of another such danger on account of some kind of mismanagement." He added that similar action had been taken to ensure the security of non-nuclear weapons.

U.S. officials said last June that the Soviet Union had begun moving tactical nuclear weapons from storage depots in regions of the country marked by ethnic conflict and nationalist tensions, such as the Baltic states and the Caucasus, and storing them in the Russian republic. The Soviet Foreign and Defense ministries denied those reports.

Appointed chief of the general staff in 1988 following the retirement of Marshal Sergei Akhromeyev, Moiseyev, 51, belongs to a new generation of Soviet military leaders who have made their careers entirely in the nuclear era. He made his public reputation with a series of articles in the Soviet military press calling for improved technical training of officers and better military discipline.

According to Western estimates, the Soviet Union possesses about 30,000 nuclear warheads, from intercontinental ballistic missile systems that can hit the United States to small artillery charges. The warheads are dispersed in hundreds of nuclear silos, naval ports, air bases and special nuclear depots.

Ironically, Western military attaches here feel relatively comfortable about the security of the 13,000 or so strategic missiles, most of which are located deep inside Russia and well-guarded by the elite strategic rocket forces. Of greater concern are the tactical nuclear warheads under the control of the Soviet army, air force, navy and air defense branches.

Keeping track of the number of nuclear warheads withdrawn to safer locations for fear of ethnic unrest has been complicated by recent disarmament moves by the Kremlin. Western experts note, for example, that the Soviet leadership has gradually been withdrawing nuclear warheads from its Baltic Sea fleet because it wants to promote the region as a nuclear-free zone.

In the past, nuclear warheads have been assigned to the Black Sea fleet stationed in the ports of Ochamchire and Poti in Soviet Georgia, which along with the rest of the Caucasus region has been the scene of nationalist disturbances. Known Soviet caches of nuclear warheads in Central Asia have included Kattakurgan in Uzbekistan, site of a battalion armed with short-range SS-12M missiles, and Baryam-Ali in Turkmenistan, a base for a brigade armed with short-range SS-23 missiles.

According to Western diplomats, contacts between Washington and Moscow over Soviet nuclear security date back to the Armenian earthquake of December 1988. Since then, worries about construction standards for nuclear warhead facilities have been overtaken by concern about ethnic turmoil, with virtual civil war breaking out on the borders between Armenia and Azerbaijan earlier this year.

Like the United States, the Soviet Union uses a system of technical codes to ensure that missiles can only be fired on the instructions of the top political leadership. One Western attache said the United States gave the Soviet Union its coding technology in the 1960s to ensure improved security over the use of nuclear weapons.

Since he became chief of the general staff, Moiseyev has called for tighter control over use and deployment of nuclear weapons. He argued earlier this year that the constitution should be amended to make clear that the president alone can approve testing of nuclear weapons and order their use in retaliation for a nuclear attack.

Moiseyev's suggestion was not adopted. But the revised constitution makes clear that the president is also commander in chief of the armed forces and responsible for Soviet national security. Before Gorbachev took power in 1985, the Communist Party's general secretary also served as chairman of the defense council, but his powers were never codified.

Some senior generals, expressing concern over nuclear security, have argued against such proposed reforms as the creation of territorial defense units in the 15 Soviet republics. Interviewed by the army newspaper Krasnaya Zvezda last July, the commander in chief of paratroops, Gen. Vladislav Achalov, asked sarcastically, "Can you imagine the existence of five, six or more 'nuclear push-buttons' in the country?"

So far, none of the republics has demanded the right to control its share of Soviet nuclear weapons. Indeed, the Ukrainian and Byelorussian legislatures both have declared their intention to create "nuclear-free zones" in their republics.

Some Western military experts in Moscow, trying to keep track of the Soviet Union's 30,000 nuclear warheads, fear that tampering with the present chain of command could have undesirable circumstances.

"When you are trying to manage an inventory of nuclear weapons with 100 percent reliability, any instability can be a problem," said one defense attache. "I don't really fear that any of the republics, even the most hot-headed ones, will challenge a declining Soviet Union by saying, 'We want our nukes.' But moving a lot of weapons around opens the door for Murphy's Law. Rather than moving them out of the Ukraine, for example, it may be better to let the darn things sit where they are as long as they are well-guarded."

In recent speeches, Gorbachev has raised the specter of "15 nuclear states" and suggested that the West has a vital interest in the future of his perestroika reform program.