The death toll in the Afghan rebel ambush of a tourist bus last Sunday rose to two when diplomats reported today that in addition to a young Canadian shot in the head, a Swiss man had also been killed as he crouched for cover on the floor.

Another tourist, Russ Anthony Shanks of Australia, is in critical condition in a hospital in Herat with multiple bullet wounds in his stomach and legs.

Survivors among the 40 European, American and Canadian passengers said that the bus, chartered by a British firm, the Masic Bus Co., had no business being in Afghanistan. The tour, from Istanbul to New Delhi, was advertised as being routed through Pakistan.

The survivors said that despite some opposition from the passengers, the Turkish driver decided at the last minute to save fuel and go through a country where a savage guerrilla war has raged for more than a year. The embassies of all Western countries are warning tourists to avoid Afghanistan unless it is vital to go there.

The tour spent Saturday night in Herat -- a city which earlier this year fell into rebel hands for a few days. At that time, captured Soviets were mutilated and skinned alive.

Shortly after dawn on Sunday, the Turkish registered bus took on board four armed Afghan soldiers as escorts, and joined a convoy of other buses and trucks for the journey along the dangerous Herat-to-Kandahar highway. There have been a number of attacks on Afghan vehicles on that road recently.

However, the Turkish driver apparently became impatient, and left the convoy to speed ahead. Forty-five minutes out of Herat, a shot was fired from the right of the bus and immediately a barrage opened up from the left.

The driver slammed on the brakes of the bus and it stopped in the middle of the ambush.

The Afghan soldiers returned the guerrilla's fire, while the driver, his Turkish co-driver and the passengers threw themselves down in the aisle and underneath the seats.

After the attack, the Turkish driver disappeared, diplomatic reports said. A Swiss tourist took over the bus and drove it back to Herat.

The latest reports bring to eight the number of Westerners murdered in Afghanistan between last Friday and Sunday.