BEIJING, MAY 15 -- It was a most unusual entrance for the head of the Soviet Bloc here on such a historic mission. Soviet President Mikhail Gorbachev had to be virtually smuggled through an obscure back entrance into China's Great Hall of the People today for what was planned as a solemn ceremony marking the first Sino-Soviet summit in three decades. Two Chinese soldiers saluted raggedly as Gorbachev's black Zil limousine, flying the red flags of China and the Soviet Union, swept past a pile of rubble into a secluded inner courtyard of the Great Hall. The Great Hall of the People has been the setting for many major occasions in modern Chinese history, including president Richard M. Nixon's landmark visit in 1972. But today it was besieged on two of its four sides by tens of thousands of young protesters calling for democracy and hailing Gorbachev as a great reformer, forcing authorities to find an alternate way in for the Soviet leader. Gorbachev's manner of arrival at the Great Hall was almost a metaphor for what will surely go down as one of the most extraordinary days in the 70 years since the first communist state was established. It seemed at times as if the center of Beijing had been taken over by tens of thousands of marching, chanting protesters, leaving the government in a state of near-paralysis. Whatever the outcome of the latest confrontation between the Chinese government and the students, today's events will be remembered as a graphic example of the difficulties faced by communist reformers. The disturbances in Beijing have largely overshadowed -- at least temporarily -- the reconciliation between the communist giants, who together cover nearly a quarter of the world's land mass and account for almost a quarter of its population. The reforms initiated by Gorbachev and China's Deng Xiaoping have caught the imagination of the outside world. But they have also unleashed unpredictable socio-political forces, as ordinary Soviet and Chinese citizens use their new-found freedoms to criticize high-level corruption and autocratic one-party rule. Without the legitimacy granted by free elections, communist regimes can seem remarkably fragile once the seemingly monolithic political facade begins to crumble. It is ironic that most democratically elected governments would probably have had fewer qualms than the Chinese authorities have displayed in clearing a public square to provide a proper welcome for a visiting world leader. Reporters were kept guessing how the Soviet leader would enter the hall. They were told first that Gorbachev would be arriving at the main east gate facing Tiananmen Square, then at the north gate, and finally at the south gate. His 30-car motorcade eventually ended up taking a little-used entrance on the west side of the hall farthest from the square, China's symbolic seat of power. Watching this scene were half a dozen Western journalists who had wandered around the back of the huge hall and encountered an unhappy Soviet security man who said he had no idea what was going on. "Ask him, we don't know anything," the security man said, pointing to a Chinese colleague who seemed equally perplexed by the schedule changes. Since the avenue leading past the Forbidden City had been taken over by demonstrators, the Gorbachev motorcade was obliged to take a detour through side streets -- past the Beijing carpet outlet and the Oriental restaurant -- to reach the seat of the Chinese legislature. At one point this evening, a group of several thousand demonstrators even tried to force their way into the Great Hall through the eastern entrance that Gorbachev had originally been scheduled to use. Hundreds of unarmed Chinese soldiers rushed out of the building to confront the protesters, who said they wanted to meet government leaders. After 90 minutes of pushing and shoving, student leaders managed to persuade the crowd to pull back from the hall, arguing that their actions might provoke a government crackdown. "Leave! Leave!" and "Come down! Come down!" the students chanted. Gorbachev, who had been exchanging toasts with Chinese President Yang Shankun during the confrontation on the steps of the east entrance, later left from the other side of the building. Onlookers cheered lustily as the Soviet leader leaned out of a window of his limousine and waved to the crowd. At a press briefing this evening, Soviet spokesman Gennadi Gerasimov dismissed suggestions that the student demonstrations raised security problems for the Gorbachev party. "Why should we worry? They are friendly crowds," he said. As more and more people poured into Tiananmen Square today, their red banners streaming in the breeze, Chinese officials could be seen on top of the Great Hall of the People gazing at the vast crowd through binoculars. The crowd filled up almost half of the square bounded by the Forbidden City and a mausoleum housing the embalmed corpse of Communist Party chairman Mao Tse-tung. While Gorbachev was inside the Great Hall, student protesters attempted to fraternize with thousands of soldiers and policemen who cordoned off the south and west sides of the building. At one point, they began throwing ice cream bars at the bewildered soldiers, provoking officers to shout "Don't eat them!" Aware that the presence of soldiers would immediately attract thousands of demonstrators, the authorities waited until five minutes before Gorbachev was due to arrive at the hall before sending in troops to seal off the area. The authorities have taken extraordinary measures to prevent a confrontation between the troops and the students, who seem to be growing more excitable the longer they camp out in the square. The soldiers and paramilitary police are not armed. Instead, they have been used to create a human wall 10 or 20 deep. To keep up morale on both sides, student activists and army officers have led communal singing, encouraging everybody to sit down to lessen the tension. The atmosphere was a strange mixture of political rally and open-air rock concert.