Although more Americans than Soviets would be immediately killed in any all-out exchange of strategic nuclear weapons, the two societies would survive in a primitive from, according to a soon-to-be-released study of nuclear war effects by the congressional Office of Technology Assessment.

Up to 165 million Americans could die, the OTA study found, and the survivors would live under conditions that would be "the economic equivalent of the Middle ages."

As for the Soviet Union, a large-scale U.S. attack against its "military and urban-industrial targets would remove that nation from a position of power and influence for the remainder of this century."

And although immediate deaths in the Soviet Union would be lower than those in the United States, there is no evidence that the Soviets would be able to rebuild an industrial society more easily than the United States, according to the study.

The OTA study was requested last September by the Senate Foreign Relations Committee and designed to provide information for use during Senate consideration of the strategic arms limitation treaty (SALT II).

Drawing on classified executive branch surveys and reports by four private research firms, the OTA study found:

In a "limited" nuclear attack against each other's strategic nuclear forces, "while the consequences might be endurable (since they would be on a scale with wars and epidemics which nations have endured in the past), the number of deaths might be as high as 20 million."

In the months and even years after the nuclear strickes, the number of deaths could equal those at the time of the attack because of starvation as well as lack of shelter and medical services.

One of the greatest unknowns is the effect of thousands of nuclear explosions on the environment. "The possibility of significant long-term ecological damage cannot be excluded," the study finds, and "some regions might be almost uninhabitable."

Bigger Soviet warheads could result in more Americans being killed. Yet the larger and more varied U.S. economy could recover more rapidly from a nuclear attack.

Though the widely publicized Soviet civil defense program is credited in the report with some saving of lives, the study's conclusion is that "it is not clear that a civil defense program based on providing shelters or planning evacuation wouldnecessarily be effective."

Conditions after the attackwould get worse before they started to get better," the study said, particularly regarding medical assistance, food, water, and shelter from long-term radioactive fallout.

Original promoters of the Study believed it would aid in getting the SALT II agreement approved. "If reminded of the horrors of nuclear war," one member of the study advisory panel said yesterday, "it was thought senators would like it less and that might help the vote."

In some ways, however, the opponents of SALT might use it to promote their idea that a nation could survive a nuclear war and thus plan to fight it. In addition, the benefits of civil defense planning, albeit small, do become apparent in each attack situation.

Take the case of a Soviet first strike against U.S. strategic weapons bases. The study estimates from 2 million to 20 million Americans would die in such an attack depending on the day, hour, time of year and "the degree of emergency preparations."

Since U.S. missile silos are away from big cities, such an attack "would cause relatively little civilian blast damage." But bomber bases and strategic submarine facilities are near cities, such as Sacramento, Calif., and Charleston, S.C.

"Little Rock, Ark., for example, the site of an ICBM base and bomber base, would receive blast damage from a pattern attack (designed to destroy bombers in flight) and intense fallout from the attack on ICBMs," the report states.

The heavy destruction from the Soviet attack stems from the presumed use of megaton-sized nuclear war-heads.

A U.S. counterforce attack would involve smaller warheads, but megaton-size bombs dropped from aircraft "would create very large amounts of fallout," according to the study.

Soviet civil defense preparations, such as sheltering, "are more extensive than in the U.S.," the study said, but "the Soviets might have more difficulty than the U.S. in improvising fallout protection" since "both frozen earth and mud could create problems."

A study by te U.S. Arms Control and Disarmament Agency shows the effect of shelters by placing possible Soviet fatalities in a counterforce attack at from 3.7 million to 13.5 million if 90 percent of the urban population was sheltered. Without shelters that number could go as high as 27.7 million, the study says.

In either a limited or all-out attack, the problems of immediate medical care would be enormous, according to the study.

To illustrate, it notes that if Detroit were hit with a one-megaton warhead, nearly 500,000 persons would be injured. Over half the 18,000 hospital beds in the area would be destroyed in the blast and 4,000 more would be damaged. That would leave only 5,000 beds, which could handle "only 1 percent of the number of injured," according to the study.

Burn victims, the study says, would be "in the tens of thousands," yet the whole United States has only 1,000 to 2,000 beds in specialized burn centres.

The Soviets would experience similar problems, the report said.

Even in peacetime, it notes, antibiotics are in short supply in the Soviet Union. "Because of the U.S.S.R.'s limited supply of antibiotics, many could be expected to die from disease that affect irradiated people," the study says.

The study presents a grim picture of life in a shelter in the first 10 to 30 days after a nuclear attack.

"People would not know if the shelter offered a sufficient protection factor," it says, "or it further attacks were imminent. The shelter might be dark . . . Unless the shelter had a good air filtration system to keep out fallout, the air would become clammy and smelly and carbon dioxide concentration would increase."

"It would be dangerous to leave the shelter for anyting but brief periods because of the radiation.

Radiation sickness, the study says, "would present special problems." Some of its symptoms, vomiting, for example, are induced by acute psychological shock of a type to be expected under attack circumstances.

"Thus, the study notes, "someone who vomited would not know if he had received a moderate, severe, or lethal dose of radiotion" or was just in shock.

Uncertainties of this type would increase tension in the shelters. Outside the shelter, fallout would be affecting both plants and animals necessary to eventual survival, the report said.

Soviet shelter dwellers would have several advantages over Americans, the study suggests. "They are more accustomed to crowding and austerity than are Americans, so would probably suffer less 'shelter shock.'"

On the other hand, the Soviets would be more vulnerable "to an attack in winter . . . Other things being equal Soviets could bring less food and supplies into shelters than could Americans.

A counterforce strike against either nation would not threaten its economic viability, the study syas. For the United State, such a strike is compared to losses suffered in the South from the Civil War that took "a century to wear off."

As for the Soviets, the counterforce attack "could be somewhat less damagaing than World War ii was . . . and Soviet recovery from that conflict was complete."

The study, however, goes on to point out that the Soviet Union emerged from that war victorious.