Lisa Wichser, an American scholar imprisoned here for a week without charges, was freed today by Chinese authorities who said she had confessed to stealing "confidential documents" and pleaded for leniency. She was ordered to leave China within 48 hours.

Wichser, 29, obviously shaken and reportedly suffering from stomach trouble, was released to U.S. Embassy officials at 6 p.m. Four hours later, she read a statement from the doorway of her guesthouse, saying, "I have always been a friend of China and I will continue to be a friend of China."

Escorted by friends and U.S. officials, she then went into the small living quarters where she had been arrested last Friday in a 1 a.m. raid. Once inside, she is said to have sobbed heavily while packing her possessions.

In her brief meeting with reporters, Wichser made no comment on the allegations against her. "I'm happy to be released, and I look forward to going home," said Wichser, whose family lives in Indianapolis.

She is expected to leave Peking Friday morning for the United States. Embassy spokesman Mark Crocker told reporters that although Wichser's "spirits have improved" since she was freed, "she said she's sick, she suffers from a nervous stomach."

Crocker said he was unaware of any confession made by Wichser, adding that U.S. officials stand by her innocence. "We're not certain what it is she's supposed to be guilty of," said Crocker.

The U.S. Embassy officially protested China's handling of the arrest, and American diplomats said today that the incident could further damage relations that already have been seriously strained by Peking's demands for an end to U.S. arm sales to Taiwan.

China's Foreign Ministry said tonight that it "categorically rejected" the U.S. complaint, which it called a "distortion of the facts."

The official Chinese news agency said Wichser had been granted leniency despite her written confession that she had "collected information and stole many of China's confidential documents." It said police found "a number of such documents" in her guesthouse rooms.

In China's highly secretive official world, almost all written material--Communist Party documents, speeches, background papers and even news analysis--is considered to be "confidential" unless it is publicly released through one of the state propaganda organs.

As a graduate student at the University of Denver, Wichser had come to China to collect data for a doctoral thesis on the Chinese rural economy. She also was teaching English.

About two months ago, she applied to Chinese authorities for permission to marry a Chinese graduate student also studying economics. The man has disappeared in recent weeks and is believed by Wichser's colleagues to have been arrested for leaking documents to foreigners.

According to a well-placed Chinese source, Wichser had obtained Central Committee materials on economic subjects. The materials had been made available to Chinese work units but were not for distribution to foreigners, said the source.

Crocker said the embassy "has made very strong representations" on behalf of Wichser during her captivity, but he refused to say whether U.S. complaints--as opposed to purely Chinese reasons--were responsible for freeing her.