The Soviet population is not protected from attack to the extent that the Kremlin could logically regard nuclear war as a risk worth taking, the Central Intelligence Agency said in a report released yesterday.

The CIA, while acknowledging that Soviet civil defense preparations have been intensifying since the "late 1960s", concluded that the Russian program has many of the shortcomings of our own, including "apathy" by "a large segment of the population."

To make a nuclear war thinkable, the agency said, soviet planners would have to evacuate their people to protect them from an American counterattack. But such an evacuation would have to take place days before Soviet missiles were launched, the CIA said eliminating the element of surprise.

In summing up whether defenses are effective enough to make Soviet leaders believe nuclear war with the United States could be a winning proposition, the CIA said. "We do not believe that the Soviets' present civil defenses would embolden them deliverately to expose the USSR to a higher risk of nuclear attack."

Sen. John C. Culver (D-Iowa), in a news conference, termed the CIA report "the first comprehensive and authoriative analysis" of the Soviet civil defense program to be made public.

Its key finding, he said, is that the expanded Soviet civil defense program does not "adversely affect the strategic balance" between the United States and Soviet Union.

Somes arms specialists have been arguing that the Soviets' improved defenses against nuclear attack, including protecting their leaders, workers and vital industries, indicate that the Kremlin is preparing to wage and survive a nuclear war with the United States.

These were other findings in the CIA's 16-page report:

The Soviet avil defense program "is not a crash effort, but its pace increased beginning in the late 1960s" and now involves a bureaucracy of "over 100,000 full-time personnel."

"A sustained effort has been made to provide blast shelters for the leadership and essential personnel, about 110,000 people," but there have been no "significant" attempts to disperse industry nor make existing factories harder to destroy with nuclear weapons.

About 12 to 24 percent of Soviet workers "at key economic installations" could be fit into existing bomb shelters, while 10 to 20 percent of the total city population could be protected from nuclear attack.

"Over 100 million" Soviet civilians would die from a U.S. nuclear retaliatory attack made under the "worst conditions for the U.S.S.R." but "a large percentage" of Soviet leaders would survive."

"Under the most favorable conditions for the U.S.S.R., including a week or more to complete urban evacuation and then to protect the evacuated population. Soviet civil defenses could reduce casualties to the low tens of millions."

Although many of the workers in bomb shelters would survive, "the Soviets could not prevent massive damage to their economy and the destruction of many of their most valued material accomplishments."

The CIA, in arriving at those conclusion, assumed that the United States counterattack would focus on factories and military installations, rather than on the Soviet population.

Culver, chairman of the Senate Armed Services subcommittee, which oversees the U.S. civil defense program, said that the United States could kill even more Soviet civilians, if there were any reason to do so, by using "dirtier" H-bombs than those now deployed and by zeroing in on the civilian population.

The pentagon, in response to the Soviets' stepped-up civil defense effort, is considering a more ambitious undertaking which Culver said could cost $2 billion over five years. The CIA estimated that it would cost $2 billion in 1976 dollars to duplicate the Soviet civil defense program in existence that year.