China, which suffered greatly from illegal imports of opium until early this century, unwittingly has become the main source of the illicit drug Quaalude smuggled into the United States, according to U.S. officials.

China is said to export legally large quantities of the sedative to free ports in West Germany through normal trade channels under its generic name methaqualone. Brokers in West Germany, in some cases working in collusion with illegal traffickers, ship the drug to Mexico, Colombia and Canada, where it gets diverted into illicit channels and eventually is smuggled into the United States, U.S. officials said.

Although American officials say they have no evidence directly linking China to illegal exports of the much-abused depressant, they blame Peking for failing to adopt commercial safeguards that could keep Quaalude off the illegal market. China is believed to produce the drug in larger quantities than anywhere else in the world.

In Washington, Gene R. Haislip, director of the Drug Enforcement Administration's diversion control office, said 80 to 90 percent of world production of the drug is consumed illegally. The DEA estimates that about 120 tons per year have entered the country illegally, most of it from Colombia, where the barrels of methaqualone powder are converted into tablet form.

Haislip said sales of Quaaludes in the United States were estimated at about $2 billion in 1980, but they have dropped somewhat this year.

Since last year, U.S. diplomats in Peking and Washington have tried to persuade China to work out arrangements with its Western European buyers that would guarantee that the drug will stay out of the hands of international traffickers.

Chinese authorities, who are eager for foreign currency to finance the nation's modernization, have told the Americans that it is up to the West German government--not Peking--to stop the illegal diversion, sources said.

"China's sale of a certain amount of methaqualone as medicine through normal trade channels fully conforms to international practice," a Chinese Foreign Ministry spokesman said in response to press inquiries this week.

The spokesman said Peking "has nothing to do with and stands resolutely opposed to the illegal narcotics traffic."

Quaalude, which is unavailable to Chinese here, is one of the most popular drugs abused by American teen-agers. U.S. drug authorities list it as the major cause of deaths, injuries and mental trauma in 13 major U.S. cities.

According to a Western diplomat here, China's production of methaqualone exceeds world demand for the drug as a form of medicine.

[Haislip said other major sources of Quaalude in West Germany, Austria and Hungary were "effectively cut off" in recent years when those governments agreed to restrict production and sales severely and to cooperate with U.S. enforcement activities against illegal traffickers.]

["We have made very substantial progress. The problem now is smaller, and of the remaining problem virtually all of this is the Chinese material," he said.]

Peking is known to be especially sensitive to questions of drug trafficking because of its own traumatic experience with opium brought to China by American and British merchants from the late 18th to the early 20th century.

Smoking opium, which is addictive, became epidemic among wide segments of the Chinese population, contributing to the demoralization and decay of the last Chinese empire, which at the time was overrun by Western colonial powers.

When opium trade began causing a serious drain on silver in the 1830s, the Qing Dynasty sent an official to Canton to dismantle the drug network. He publicly destroyed about 20,000 chests of opium brought by British merchants.

Britain went to war over the loss of the opium, seizing large stretches of the Chinese coastline before the emperor surrendered in 1842. China was forced to pay for the damaged drug and guarantee the British generous trade concessions.

Although the current Communist government has abolished use of narcotics, it still points to the old opium trade as a classic symbol of Western colonialism and capitalist exploitation of innocent Chinese.

Appealing to this Chinese awareness, U.S. Sen. Paula Hawkins (R-Fla.), who is chairman of the Senate drug enforcement caucus, has written Communist Party Vice Chairman Deng Xiaoping urging strict export restrictions on methaqualone.

She called on Deng to join other producing nations in blocking illegal shipments of the drug, charging that China "now produces about 100 percent of the methaqualone illegally used in the United States."