LHASA settled into an uneasy calm yesterday as police and plain-clothes agents patrolled the city to prevent renewed turmoil after two days of anti-Chinese riots by Tibetans, according to Western travellers in the Tibetan capital. Many shops stayed closed and the presence of undercover security agents created an atmosphere of intimidation, they said. ''It's an eerie quiet,'' said one European. ''Normally there are a lot of people on bikes, in cars, and wandering around the stalls. Normally it's crowded around Barkor,'' he said, referring to the main square in Lhasa. Many of the Chinese and Tibetan stalls around the Barkor were closed yesterday, although department stores and Chinese-run shops in other parts of the city were open for business. Jokhang temple, the holiest of Tibet's Buddhist shrines, was open, but the numbers of people arriving to worship was far fewer than normal. The presence of uniformed security forces yesterday was scaled back from Tuesday, when, according to one traveller, ''police were at every corner''. However, undercover agents seemed to be out in force following the protests. ''It's really unpleasant,'' said one Swiss traveller. ''There are so many plain-clothes . . . asking so many questions. You need to take care when you speak. It is difficult to know who is a policeman.'' A number of foreigners had their visas cancelled for taking pictures during the protests or for simply having been seen walking the streets with cameras. One European said police forced him to write a self-confession, fined him 600 yuan (HK$809), and gave him until today to leave China because he had allegedly participated in the demonstrations and taken pictures. The foreigner said he had merely walked beside the protesters and had taken no pictures. He knew of at least three other foreigners being expelled this week for having taken photographs of the demonstrations. Their film had been confiscated. This week's protests were stifled with tear-gas and numerous arrests, according to travellers. Many foreigners said they had heard talk of a child being badly injured, possibly killed, when a tear-gas canister blew up in its face during the protests. A source at the Lhasa Holiday Inn said the recent unrest had not affected the arrival of foreign tourists. A flight from Nepal was cancelled on Tuesday, but only because of strong winds. Other tour groups were coming in as scheduled, and were able to visit all the major tourists sights. The Public Security Bureau had posted a notice in the hotel instructing foreigners on what to do in case of an uprising. The notice advised tourists to be cautious, obey regulations, and not participate in any protests. Meanwhile, the London-based Tibet Information Network said yesterday that it had obtained a letter written by Gendun Rinchen, one of those arrested, that said he had planned to present a letter on human rights violations in Tibet to the delegation of European Community ambassadors that left Tibet earlier this week. The letter was dated April 16 and was written to a friend. The group quoted sources in Lhasa as saying the ''state secrets'' Rinchen, a tour guide, and Lobsang Yonten, a former monk, were accused of stealing were lists of Tibetans imprisoned for taking part in demonstrations. In his letter, Rinchen said police were torturing detainees. Some were so badly treated that when they were transferred to other detention centres, prison guards refused to take them. Rinchen said he decided to write the letter after seeing how an earlier US delegation had been monitored so closely, they could not meet ordinary Tibetans. ''Their visit was not worth anything, except that they might have experienced what it is like, living like a criminal,'' the tour guide said. ''If the Chinese treat them in such a way, then they can imagine how they treat us.''