The Central Intelligence Agency is "almost certain" that Afghan troops massacred hundreds of civilians in eastern Afghanistan last year under instructions from Soviet advisers, according to CIA Director Stansfield Turner.

In a letter to Sen. Lloyd Bentsen (D-Tex.), Turner listed several other alleged atrocities -- "with details omitted to protect our sources" -- that have come to the CIA's attention in the past year.

Bentsen, who released Turner's report last week, urged President Carter to seek an investigation by the United Nations or another international organization.

Bentsen wrote Turner last month inquiring about a Feb. 4 article in the Christian Science Monitor concerning the reported murder of 1,170 men and boys in the Afghan town of Kerala, not far from the Khyber Pass, last April 20.

A similar dispatch from Agence France-Presse appeared in The Washington Post. According to the reports, based on interviews with several of the widows, the villagers were told to proclaim their support for the Marxist regime and then were shot when they responded with Moslem sayings.

The troops, reportedly including about 20 Soviets in Afghan uniforms, then used a bulldozer to bury the victims, some still alive, the reports said.

Turner said the CIA had no "on-the-spot confirmation from our own sources," but pointed out that a strikingly similar account, putting the death toll at 1,300, appeared in a Pakistani newspaper last April 29.

The CIA director's letter, which he told Bentsen could be made public, appeared to reflect a concerted effort by the agency to expose Soviet-backed brutality in Afghanistan.

Other reported incidents that Turner cited included:

The slaying of 20 villagers who refused to cooperate with the Kabul regime and the destruction of their village by Afghan troops. "The children among the victims were mutilated in front of their parents before the entire group was slain," Turner said.

The killing by Afghan soldiers of the 300 people in another village, reportedly for "noncooperation."

Instances of aggravated rape by Afghan soldiers, some resulting in the victims' deaths.