PARIS, AUG. 1 -- The sudden vehemence with which the Soviet Union has pinned the fate of a historic superpower arms control agreement to the destruction of 72 U.S. Pershing IA nuclear warheads has stunned U.S. negotiators and others who thought the agreement had come within easy reach.

Behind the public campaign by the Soviets against the 72 antiquated warheads stationed in West Germany lie at least three interrelated factors, conversations in recent weeks with Soviet and American officials in Moscow, Washington and Western Europe suggest:Negotiating tactics. The Soviets have adroitly whipsawed the American side by generating bursts of optimism with apparent Soviet concessions and then escalating specific demands.

Thus, they have positioned themselves either to get the deal they want or to harvest gains in world public opinion by blaming a breakdown on apparent American unwillingness to give up relatively insignificant nuclear weapons.

Shift in military doctrine. If the deal does go through, the Soviets can offer significant military reductions in return for political gains because party leader Mikhail Gorbachev appears to have persuaded his military to accept a doctrine of "reasonable sufficiency" in nuclear weapons.

Pursuit of a long-term drive to make the Soviet homeland as safe as possible from nuclear attack. Removal of all U.S. nuclear warheads from land-based missiles stationed in Western Europe represents a psychological watershed for the Soviets, many American officials argue.

It is the psychological factor that is perhaps most difficult for Americans to grasp, unless they are familiar with the heavy emphasis that Russians place on the loss of 20 million Soviet citizens who are said to have perished in the World War II campaigns on Soviet soil.

Moreover, even if the Pershing IA warheads were destroyed along with Pershing II and Tomahawk cruise missiles under the agreement now being negotiated at Geneva, there still would be thousands of warheads aboard U.S. aircraft and submarines in Europe and land-based strategic missiles in the United States that would threaten the Soviet Union.

But many U.S. officials who have intensely studied the philosophy and practice of nuclear deterrence are convinced that the Soviets lay particular emphasis on eliminating U.S. land-based rockets and warheads from Western Europe because of the reliability, effectiveness and speed of this category of weapons.

"Ships can sail away, and planes can fly away in a crisis," a senior U.S. arms control negotiator said. "Land-based nuclear weapons are the most solid form of America's commitment to halt a Soviet attack on Europe, and the Russians will be achieving vertical denuclearization of Europe if they get all of our nuclear missiles off the continent."

"The Soviets have to understand that they will suffer more pain than gain and that their territory will not be a sanctuary if they attack," Gen. Bernard W. Rogers said in an interview shortly before retiring as NATO commander in chief in June. Rogers said losing Pershing IIs and IAs would seriously damage NATO's ability "to keep the pain felt by the Soviets as high as we can."

Soviet diplomats speak of "reach criteria" as a major component of their arms control strategy. By this they mean the superpowers' placing priority on reducing or eliminating nuclear weapons that can reach each others' territory.

The range of the Pershing IA, which the United States maintains is a hybrid weapon with an American warhead and a West German booster rocket and, thus, not subject to the U.S.-Soviet treaty under negotiation, is generally given as 460 miles.

But allied arms control officials acknowledge that the range of nuclear-tipped rockets is a far more imprecise matter than such concrete figures suggest. The actual range when fired will depend on fuel load, atmospheric conditions and other unpredictable factors, these officials say, adding that they routinely estimate that such missiles may travel 30 percent farther than their stated range under favorable conditions.

The IAs probably would be able to hit Soviet territory and certainly would be able to hit Soviet units stationed in Eastern Europe.

"These warheads carry 200 to 400 kilotons of destructive force," Col. Gen. Nikolai Chervov, the Soviet Defense Ministry's senior arms control adviser, said in an interview in Moscow this week. "They have the equivalent force to destroy 72 cities."

Chervov emphasized that the Soviet military had taken to heart Gorbachev's demands for "new thinking" in foreign and military policy and was willing to give up 441 SS20 missiles and 130 shorter-range missiles as part of a move to achieve "reasonable sufficiency" in nuclear weapons.

In the past, Soviet military commentators have emphasized Soviet determination to obtain and preserve nuclear parity with the United States.

The proposed medium- and shorter-range missile accord, covering missiles with medium ranges of 600 to 3,500 miles and shorter ranges of 300 to 600 miles, "is a manifestation of our defensive-oriented military doctrine" as outlined by Gorbachev in a speech in East Berlin in June, Chervov said.

Chervov and Deputy Foreign Minister Alexander Bessmertnykh strongly emphasized that the Soviets were only concerned about adding the Pershing IA warheads to the accord. Stressing that the Soviet Union already had made a major concession in agreeing to leave British and French nuclear missiles out of the agreement, Bessmertnykh said, "We are not touching the missiles" that carry the warheads. "They are German. The warheads are American and must be included."

Chervov acknowledged that he had questioned U.S. negotiator Maynard Glitman about the Pershing IAs in a lengthy conversation in Geneva on June 20, but he stoutly denied reports that he had suggested a compromise based on an American pledge not to modernize the aging warhead.

While some American officials believe that differences within the Soviet camp account for a pattern of dramatic turnabouts in Soviet positions in recent weeks, many others think that the Kremlin is effectively whipsawing the Americans at the bargaining table.

The optimism that the Chervov-Glitman conversation inspired quickly gave way to pessimism in Washington generated by a Soviet failure to schedule a foreign ministers' meeting, as expected, in July.

Gorbachev dispelled that mood last week by agreeing to the U.S. "global double zero" proposal, the total elimination of medium- and shorter-range missiles in Europe and Asia, and giving the green light to a foreign ministers' meeting in Washington in September.

That led President Reagan to deliver personally a statement in which the United States agreed to the destruction of all missiles and warheads covered by the agreement, a point that the Russians had insisted on.

At almost the same time that Reagan was making that announcement, the Soviets were beginning their campaign to make the Pershing IA the next obstacle that had to be resolved, on their terms, to seal the agreement that would clear the way for a Washington summit and perhaps for a trip to Moscow next year for Reagan.