OUTSIDE ARZAMAS-16, Central Russia --The sign pointing left at the junction said "dead end" but at the end of the road there was a huge red-brick guard post and a double barbed-wire fence. A troop of armed soldiers was marching through the gate of Russia's secret nuclear city.


On the face of it, security was still tight Tuesday outside Arzamas-16, the cradle of the Soviet atom bomb, three days after two men were caught stealing uranium there. Residents must show their pass to enter the city, which is still closed to most Russians and foreigners who do not have top-level clearance.


But in the last two weeks the city -- one of the main test centers for Russia's nuclear weapons program -- has come under intense scrutiny. Wilhelm Gmelin, director of safeguards at Euratom, the European Union's nuclear watchdog, said that six grams of very high-grade plutonium seized in Germany in May may have originated in Arzamas-16.


Itar-Tass reported Wednesday that two men had been caught Saturday trying to steal 9.5 kilograms of low-grade uranium-238, which is not used to make nuclear weapons, from Arzamas-16.


The closed city's deputy mayor, Valentin Mamyshev, contacted by telephone Wednesday, confirmed the seizure but said he was satisfied with security arrangements in the town.


"We have not had to make any additional security measures," Mamyshev said, when asked if security had been stepped up since the seizures in Germany. "We have the usual entrance and exit procedure. As far as I am aware this is the first case we have had."


But local people and residents of Arzamas-16, which is still not to be found on any map, said scientists, who once spent years locked inside the city, were traveling freely in and out and that the strict system of monitoring them appeared to have broken down.


Yury Bragin, a former physicist, still lives in Arzamas-16 but he commutes every day from the city to Diveyevo, the village nearby. On the way he drives through a new dacha-settlement of 12,000 plots, where Arzamas residents tend vegetable plots.


"We can travel as we never could before," said Bragin, when asked about security at the city. "But all our friends are still in place."


Bragin, who has a physics doctorate, worked for 12 years as a radio-physicist in the city but now he runs a small brewery in a nearby village.


"Science is finished," said Bragin, 36, bringing his guests glasses of foaming beer. "Most of the active people have gone into business. A lot of the young people have left."


Bragin said scientists earned between 300,000 and 500,000 rubles, but were almost never paid on time. In June last year a group of scientists wrote an open letter to President Boris Yeltsin, warning the nuclear city would be close to collapse without more funding.


"There have not been any steady improvements," Mamyshev said, asked if the letter had had any effect. "Salaries are being raised but there is still a delay of a month and a half in payment."


It was not always like this. Founded in 1946 by Stalin's chief henchman Lavrenty Beria, Arzamas-16 was the Soviet Union's Los Alamos, the heart of the country's nuclear-weapons program. Of a population of 80,000, over a quarter were scientists working in the town's Institute of Experimental Physics. Andrei Sakharov worked here for 16 years.


"They used to live like kings compared to us," said Sergei Metla, the mayor of the neighboring town of Arzamas.


The 10 secret atomic cities, with 700,000 inhabitants, were always supplied directly by Moscow. While the rest of the country was grappling with shortages, Arzamas-16 did not lack for bananas, oranges and chocolate.


The 285-acre city was a kind of Soviet utopia with fragrant pine woods, a stadium, a theater, palaces of culture, well-equipped hospitals and tennis courts.


Along with that came a bizarre and obsessive secrecy. Arzamas-16 has a telephone code, 83130, but it is not listed in any reference book. Born in a place that officially did not exist, Bragin said his place of birth on his residence permit was listed as "Leningradsky Prospekt, Moscow." The town football team belonged only to a "League of Closed Cities," which played only each other.


With the end of the Cold War and the breakdown of the Soviet economy, this all changed. Igor Gordeyevtsev, editor of Arzamas' newspaper Arzamasskaya Pravda, said that in 1992 he met the head of the world's largest laboratory who spent evenings digging potatoes for his family.


Economic necessity has forced the town to come out of the shadows and make contact with its neighbors.


"Our relatives went off and we wouldn't see them for years," said Yury Kondyrev, administrative head of Diveyevo, speaking of the 1950s when the city was completely off-limits. Kondyrev has put up a radiation monitor on a shop in the main street to reassure villagers.


Gordeyevtsev said that their secret neighbor had seemed especially menacing during the Cuban Missile Crisis in 1962, when the two superpowers came closest to a nuclear war.


"Of course we were afraid because the first nuclear strike would have landed here and there would have been nothing left," Gordeyevtsev said.


The fear was reawakened in 1988 when an explosion at Arzamas railway station devastated a wide area and killed 91 people. The train carrying explosives was two minutes behind schedule outside the station, where a train from Arzamas-16 carrying radioactive material was standing."Two minutes later and the whole city would have blown up," said Gordeyevtsev, who has spent years researching the accident. "We would have had another Chernobyl. Our Russian unpunctuality saved us."