BEIJING, SEPT. 20 -- Two days before the start of the first major international sports competition ever held here, police are nervously trying to track down 21 Chinese who have threatened to sabotage the event or assassinate Communist Party leaders, a high-level government official said today.

Many Western observers doubt that violent protests will occur during the 11th Asian Games, which begin Saturday and run until Oct. 7, but Chinese authorities here are worried about the 21 persons they so far have been unable to find, the official said.

The Communist government, which hopes that a successful staging of the sports extravaganza will help restore China's tarnished image after last year's massacre of demonstrators for democracy here, did not publicly release the information about the 21. It is a concern that the government would not appear to want publicized, for fear it could reveal seemingly inadequate security arrangements prior to the games and create fear among the public.

The official said the threats were made to retaliate for the crushing of the democracy movement, and came in letters addressed to the games' organizing committee, public security organs and Beijing Mayor Chen Xitong.

All of the letters, which numbered more than 21, were signed with real names, the official said. In each case, authorities went to the locations listed as addresses in the letters, ascertained that the writers existed and in some cases learned that they had reputations as trouble-makers, the official said. All of the letter writers were detained except for the 21 still being sought, the official said.

Writers of some of the letters "vowed to sacrifice themselves" to sabotage the games, the official said, and one writer from Hubei Province in central China threatened to kill Premier Li Peng.

"The police are very, very nervous," the official said.

Chinese authorities had said only that unnamed "hostile elements" have threatened to disrupt the games, but had not revealed specific threats. At an emergency public security meeting today, a list of 21 names was distributed to Beijing police, the official said.

For the leadership, the Asian Games represent a chance to present China's best face to the world, but a Western diplomat said he doubted that the event will help improve China's internal political and economic situation.

"They will try to trumpet the games as proof that the place is stable," the diplomat said. "But after it's all over, the economy will still be in a mess, the budget deficit will be hemorrhaging, and the {political} succession question will be as murky as ever."

Chinese authorities have been working frantically for the last few months to prepare the city for an expected 100,000 foreign tourists and nearly 7,000 athletes from 37 participating nations.

The Olympic Council of Asia, which oversees the games, voted tonight to expel Iraq from the competition as punishment for its invasion of Kuwait.

Tonight's emergency meeting began with a moment of silence to commemorate one casualty of the Aug. 2 invasion. Sheik Fahad Ahmed Sabah, brother of Kuwait's emir, was killed defending the royal palace from Iraqi troops. He was president of the Olympic Council of Asia. Every delegate rose in tribute to the slain president, including Iraq's representatives.

Despite the rush of last-minute preparations, China's main preoccupation appears to be with security. Earlier this week, the Hong Kong distributors of M&M chocolates, a division of the McLean, Va.-based Mars Inc. and a games sponsor, received an anonymous letter warning that a packet of the candy had been poisoned. "M&M chocolates, which called itself the official sponsor of the games, is guilty of supporting the illegal regime," the letter said. The candy has been removed from shelves in Hong Kong, but will continue to be sold in Beijing, a company spokeswoman said.

Additional police recruits have been rushed through training to beef up security forces. Police have set up nighttime checkpoints throughout the city, especially around university campuses. Helicopters in recent days have made repeated sweeps around Beijing and Qinghua universities, which were at the forefront of last year's demonstrations. Students there have been warned to keep quiet during the games.

Nonresidents of Beijing need special permits to enter the capital. Vagrants, beggars and transient laborers have been ordered out of the city. Mentally impaired and mentally ill people have been confined to their homes or state-run hospitals.

And, in a measure of how far the authorities are willing to go to head off potential embarrassments during the games, hospitals were notified that all corpses were to be cremated by early this week. Authorities were afraid that families might try to take advantage of the international spotlight on Beijing by resorting to an unusual form of protest over unresolved claims against the government or other parties for compensation in the death of their relatives -- parading bodies through the streets. Chinese do not allow their relatives to be cremated until all disputes arising from their deaths are resolved.

To spruce up the city, millions of flowers have been planted along major streets. New walls, some painted to look like brick, have been erected to hide rundown homes. Banners and billboards throughout the city proclaim "Unity, Friendship, Progress," the theme of the games. In Tiananmen Square, on which last year's protests were centered, two giant peacocks and two statues of Panpan, the panda mascot of the games, face off across from the huge portrait of Mao Zedong.

Official newspapers report that groups ranging from grammar school students to prison inmates have responded enthusiastically to the government's calls to bring honor and glory to the motherland by supporting the games. According to one report, parents in a small farming village of Shandong Province, in a burst of patriotic fervor, named 21 babies Yayun, which means Asian Games in Chinese.

The government appears to be trying to recreate the festive atmosphere that pervaded Beijing last year during the demonstrations for democracy. But many residents say the games' expense is exorbitant, especially at a time when the state has told its 1.2 billion citizens to tighten their belts. They are unhappy, too, with the traffic regulations, tight security reminiscent of martial law and increased propaganda that will disrupt their lives for the next two weeks. Most "want nothing to do with the games," said an intellectual.

Workers in Beijing complain that they had up to one month's pay deducted from their salaries as "voluntary contributions" to the games, or that they have been forced to join "voluntary work brigades" to help construct the games' village.

Funding for the festival has been affected by last year's turmoil, Chinese officials acknowledge. The cost of the construction of stadiums, housing for the athletes and operating expenses is estimated at $530 million. Sponsorship by Chinese and foreign companies has been unenthusiastic.

Construction of the Asian Games village, a complex of sports arenas, apartments, a restaurant and hotel, has been constantly behind schedule despite round-the-clock efforts of workers and soldiers assigned to help build it. Beijing's vice mayor and a top organizer of the games, Zhang Baifa, acknowledged that China had not done well.

Many of the problems, he said, stemmed from the poor quality of Chinese-made products. In the athletes' apartments, for example, all of the 1,400 Chinese-made electric fans had to be replaced with imports after two fires broke out because of faulty equipment. At the Collegiate Stadium, site of the basketball competition, $38,300 worth of defective light bulbs had to be replaced after only eight practice matches, he said.