MOSCOW, JULY 17 -- An avalanche swept 40 climbers from five nations to their deaths in Soviet Central Asia in one of the world's worst mountaineering disasters, a Soviet official said today.

The 27 Soviets, six Czechoslovaks, four Israelis, two Swiss and one Spaniard were camped on a ledge known as the "frying pan" located 19,500 feet up in the Pamir mountains.

The avalanche struck Friday and was apparently set off by an earth tremor.

"This is the worst tragedy in the history of Soviet mountaineering, and I think, of world mountaineering," said Vladimir Shatayev, head of the Soviet State Sports Committee's climbing department.

The worst previous disaster on record occurred in 1952, when 40 people were reported killed on a Soviet expedition to Mount Everest, although the number of deaths was never officially confirmed.

Friday's avalanche struck on the slopes of 23,405-foot Lenin Peak, the second-highest mountain in the Soviet Union. It is located on the border between Tajikistan and Kirghizia and near the Chinese frontier.

In their first announcement, the Soviet authorities reported 43 mountaineers killed. But rescuers later found three survivors, two of whom were taken to a hospital, according to a sports committee spokesman.

Little information on the disaster was available from the region, as rescuers were hampered by heavy snow and the bodies had yet to be recovered.

All but four of the Soviet climbers were from Leningrad. Among the dead was one of the Soviet Union's best-known mountaineers, Leonid Troshchinenko.

Shatayev said the ledge had been used as a campground by climbers since the 1930s. "There have been camps at that site practically continuously since 1974, sometimes with 100 or more people," he said, "so nobody could have anticipated what happened."