BEIJING, OCT. 27 -- Police conducted regular nighttime arrests of suspected dissidents over a two-week period following the recent outbreak of anti-Chinese protests in the Tibetan capital of Lhasa, according to a report from western travelers received here yesterday.

The written report, dated Oct. 22, said armed police continued to patrol Lhasa at night and that police wearing helmets and carrying shields and stun guns made periodic shows of force in the city of 160,000 people during the day.

The western travelers, who asked to remain anonymous for fear of reprisals from the Chinese authorities, are sympathetic to the Tibetan independence cause. They sent their report on events in Lhasa, now under a virtual blackout, to foreign news agencies.

{In a separate development, about 150 tourists became snowbound in buses en route from Lhasa to Nepal and urgently need help, a Canadian said today. He said he left the group and hiked for five days to reach Katmandu, according to an Associated Press report from the Nepalese capital.

{At least three Americans were reported to be on the buses. The Canadian, Fred Brooks, said three buses carrying tourists have been stalled in snow since Oct. 19 following a blizzard.

{The State Department said that based on partial information, only about six to 10 travelers still remained marooned in the area. The rest had backtracked to Lhasa and the Tibetan market town of Shigatze.}

No new proindependence protests have been reported in Tibet since three demonstrations in September and this month. At least six Tibetans, including three Buddhist monks, were killed.

Authorities have curbed foreign travel in Tibet.