BUCHAREST, ROMANIA, DEC. 29 -- Down below the Communist Party Central Committee building from which Nicolae and Elena Ceausescu controlled Romania for 24 years, the doors to the underground world of the Securitate secret police are made of armored steel plate. Behind those three-inch-thick doors are offices and apartments, weapons and ammunition, a communications center, a bomb shelter and refrigerators filled with meat. They belonged to the Securitate's "Fifth Directorate" -- Ceausescu's personal guard, an elite force that fought on after the death of their leader. They fought all this past week, and the army said today a few are still down there fighting. They dress in black berets and black jumpsuits with red silk stripes on their sleeves. They carry small two-way radios and speak into them in a coded language. They are armed with automatic rifles equipped with infrared night scopes for sniping. According to an army lieutenant major who has fought against them for a week, "They are very good shots. They shoot only for the head. Their accuracy is fantastic." As the new Romanian government consolidates its power -- army tanks withdrew from central Bucharest today after several days of near calm on city streets -- learning about the size and the character of the Securitate secret police has become a national obsession. It was the Securitate -- a force Ceausescu created to protect himself and his family from a populace that hated his regime -- that shot hundreds of unarmed civilians and hundreds of army soldiers in the days after Ceausescu was toppled. The execution of Ceausescu and his wife Monday seemed to weaken the Securitate's reign of terror in Bucharest and other cities across Romania. Cazimir Ionescu, a vice president in the interim government, called the National Salvation Front, said today that thousands of Securitate members turned themselves in Thursday. But there are still several hundred highly trained commandos at large, Ionescu said. Confessions of those who surrendered have led the army to believe that the Securitate members still at large are men sworn to fight to the death. One prominent member of the National Salvation Front, Silviu Brucan, said he expected these remaining Securitate men to stop shooting civilians in the street and begin aiming their rifles only at government officials. "They realize they have been beaten and we expect them now to focus on the center, to decapitate the movement, to kill the leaders of our movement. Therefore, I have been traveling in Bucharest only in a tank for the past three days," Brucan told the British Broadcasting Corp. "I can tell you one thing. Every time I moved, the tank was shot. They know I am inside." The government today extended its deadline for Securitate members to surrender rather than face a military tribunal and a firing squad. It was the third extension in five days. Branching out from the Central Committee headquarters -- which extends three stories deep and has a command center at its bottom level -- is a labyrinth of tunnels beneath Bucharest. One connects the Central Committee building with the nearby Palace of the Republic, where other Securitate members were stationed. Another, about one-third of a mile long, goes to the army officers' club. Another connects to one of Ceausescu's homes. How many others there are and where they go are still to be learned. The lieutenant major, who did not want to be identified, said that members of the "Fifth Directorate" are still in the tunnel and that the army has not had a chance to explore the entire network. "It might be even bigger than we have discovered. At this point we don't know," the officer said. The Securitate, an organization that a Western diplomat said had about 60,000 members, was the favorite military wing of the Ceausescu regime. According to Brucan, a former ambassador to Washington and the United Nations who fell out of favor with Ceausescu early this year after writing an open letter critical of his regime, the government here spent about three times as much per soldier on Securitate forces as it spent on the army. Brucan said there was a "deliberate downgrading" of the army by the Ceausescu family so that it could arm a more loyal security force with the best American and Japanese communications equipment and weapons. Some of this equipment, Brucan said, was purchased with money drawn from the $1.1 billion that the Ceausescu family kept in foreign bank accounts. Contradicting a widespread belief among Romanians, Brucan said the elite of the Securitate were not orphaned children raised by the security apparatus. Rather, he said, they were relatively well-educated Romanians who were well paid to soothe Ceausescu's overriding worry. "He was preoccupied with a war against his people," said Brucan. Most of the members of the Securitate belonged to a mundane, above-ground bureaucracy that helped the Ceausescu family keep track of routine security matters in a rigidly closed society. These Securitate officers routinely questioned Romanians who wanted to travel abroad, who had contact with foreigners or who had been reported by informers as enemies of the state. Securitate bureaucrats filmed people believed to be dissidents and used long-range microphones to catch their conversations. When the revolution came to Romania this month, nearly all of this bureaucracy capitulated. The Securitate officers gave up shortly after the army refused to shoot civilians and joined the new leadership. The part of the Securitate that did not give up consists of at least two much smaller units. A Western diplomat said there is a 2,000-strong anti-terrorist group, called USLA. The army speaks of the even more elite presidential unit, the "Fifth Directorate," which wears the black jumpsuits. In the Central Committee building today, the army lieutenant major and another soldier -- who have been fighting against members of the presidential guard, holed up underground -- described at length what they saw and did in the past week. They led three reporters down to the first level of the headquarters, a brightly lit series of rooms separated by armored steel doors and threaded with electrical wiring and air ducts. One of the concrete-walled rooms had a refrigerator full of beef, something that Romanians almost never saw in stores under the Ceausescu government. The underground Securitate rooms -- which had been a state secret, kept even from the army -- were discovered a week ago when the army joined anti-Ceausescu demonstrators in the streets. Civilians and soldiers stormed into the Central Committee building to find a secret staircase that kept leading downward. But the extent and the sophistication of the Securitate installation beneath the Central Committee were not well understood until last Saturday, a soldier said today. That was when the son of an architect who designed the underground rooms -- apparently fearing retribution from the new government -- came forward with architectural drawings. Equipped with the drawings, the army began fighting its way down. The lieutenant major said that soldiers discovered the well-equipped bomb shelter with machines for filtering air and water, as well as a room for decontaminating people and equipment exposed to radiation. On the third level, the lieutenant major said, they found the large command center with a wall-length console of buttons and switches. These rooms were not shown to reporters today because the lower levels of the headquarters are not yet secure, the officer said. "From the very first moment we entered these rooms, most of the equipment was destroyed, either shot or smashed," the officer said. He did not want his name used because he feared retaliation from the Securitate. This is not a misplaced fear. This week, more than 10 soldiers standing guard at night in Palace Square, which stands in front of the Central Committee building, were shot fatally in the head. An editor at the state television station, Ion Simion Pop, was apparently followed home by Securitate members Wednesday night. He was shot and his body was thrown from a window of his apartment. Describing the fighting methods of the Securitate, the lieutenant major said that when fighting began a week ago, "They disguised themselves as army troops and they infiltrated among the soldiers." He said they shot several soldiers in the back. In the days of street fighting that followed, he said, Securitate forces played tape recordings of gunfire over hidden speakers to confuse soldiers into firing their weapons. Many soldiers were then picked off by snipers. A 22-year-old militia member named Doril said today that in the fighting that went on in the underground headquarters, members of Ceausescu's personal guard demonstrated expertise in the martial arts. One black-suited man, when cornered at gunpoint, managed to push away the barrel of a soldier's rifle and kick the soldier in the throat, Doril recalled. The man finally was shot to death by two other soldiers, he said. In the fighting beneath the Central Committee building, Securitate members have killed two army officers and four soldiers, the lieutenant major said. He would not say how many presidential guards have been killed or captured by the army. But he said those whom he saw captured this week resisted. "Even if they were captured alive and unarmed, they attacked the soldiers. They tried to hit the soldiers with their fists or anything they could find. They did not care anything about dying," he said. "Those captured alive have refused completely to talk, to eat, to drink water. My personal opinion is that they do not look like intelligent men. They look like robots." Soldiers coming into the underground room a week ago found the bodies of several black-suited men who appeared to have shot themselves to death. Doctors said there were about 15 Securitate commandos among the 679 wounded Romanians admitted for treatment this past week at the main emergency hospital in Bucharest. "They had a very strange behavior," said Andrei Firica, a doctor and the director of the hospital. A number of them appeared to be drugged, he said. The pupils of their eyes were dilated. He also said they demonstrated extraordinary physical strength and unusual resistance to the effects of sedatives. It took six orderlies and doctors to wrestle one of the Securitate men to the floor of a hospital corridor, he said. Two Securitate members died "completely unexpectedly" in the hospital, Firica said. "One had a broken ankle and the other had a minor gunshot wound in the shoulder." Firica said doctors did not have any idea why they died. Their teeth were checked for cyanide tablets when they were admitted. Because of the flood of patients, there was no time to perform autopsies on the two men. The few Securitate patients who spoke at all -- the last one was taken from the hospital by the army on Thursday -- were wildly defiant, Firica said. "I am sorry because I did not do everything possible to kill everyone," a Securitate major was quoted by a doctor as saying while he was handcuffed to a hospital bed this week.