For this series of three articles, Murrey Marder, senior diplomatic correspondent of The Washington Post, interviewed scores of American policymakers and Soviet officials in Washington and Moscow.

Diplomats estimate that it takes on the average about 18 months for the Soviet Union and a new government in Washington to become familiar with each other's operating style. But that by no means represents a grace period, for often the required knowledge comes out of a crisis.

The first months of a new administration are always a hazardous probing period between the two superpowers, especially if there are tensions on the international horizon. Tensions will crowd the Reagan administration's agenda the day it takes office, from Poland to the Persian Gulf where American-Soviet interests clash.

With the new administration's first priorities reviving the national economy and strengthening defense, it will be hard-pressed from the outset to gain time for designing its projected fundamental change in Soviet policy.

Few administrations have begun their term with a task of comparable magnitude. The Reagan administration will question the basic doctrines and strategies on which the United States has operated for a generation. At the same time, it will be unable to shake free easily from the crumpled structure of a decade of American-Soviet detente, because ongoing American policy, as well as the policy of the western allies, is tied to that structure.

The challenge is infinitely more complex than any campaign statements foreshadowed, and Ronald Reagan's Cabinet contains only one member with any operational experience in superpower relations, Secretary of State-designate Alexander M. Haig Jr.

Many Reagan advisers are calling for some form of "containment" of the Soviet Union, to prevent it from projecting its military power, by coordinated use of western military, economic and political strength. Neither the president-elect nor Haig has yet indicated a public position on an outright containment policy, although both seek greatly intensified resistance to Soviet power.

Whatever new military strength the United States adds, it cannot recover the nuclear supremacy or political authority it relied on to wall off the Soviet Union during the Truman-Eisenhower containment years of the late 1940s and 1950s.

Reagan apparently recognized that when he substituted the goal of "a margin of safety" for the Republican platform pledge to reestablish American strategic "superiority" over the Soviet Union. The euphemism is more palatable in international discourse, although the nuclear age allows no real margin of safety to either superpower.

In formulating its policies, the Reagan administration is committed to consult closely with Congress and with America's allies. With Republican control of the Senate, and new Republican strength in the House, the Reagan administration will have considerable support for stiffening U.S. policy toward the Soviet Union in the current climate of American opinion.

The Western European nations, however, will resist any made-in-Washington strategy for hardening East-West relations, as former general Haig can attest from his recent years as supreme allied commander of NATO. President Carter gained only ragged Allied support for his attempts to exact "a concrete price" for the Soviet invasion of Afghanistan, although the North Atlantic Treaty Organization is pledged to firmer reaction if the Soviet Union resorts to force in Poland.

The most intricate issues ahead are imbedded in the intended strategic arms limitation treaty, SALT II, which Reagan has rejected in its present form as a wholly inadequate restraint on Soviet power. Reagan, by insisting that limitations on the Soviet Union's global use of force must accompany any arms control accord, has made this the central issue in his Soviet policy.

In developing its strategy, the Reagan administration is challenging American doctrine dating back to the 1960s. One of the basic concepts that the United States adopted in those years was that strategic stability would be achieved between the two superpowers if their intercontinental nuclear forces were relatively equal. It became the American objective to level off opposing forces at "parity." But behind the supposed equilibrium of "parity" there were layers of unforeseen instabilities.

One major impact of "parity" came in Europe. Western defense had relied primarily on American nuclear superiority to deter the larger conventional forces of the communist nations of the Warsaw Pact. With the United States and the Soviet Union having approximately equal nuclear forces, the American nuclear advantage for western defense was gone, progressively raising alarm that NATO nations were becoming increasingly vulnerable to communist attack.

At the broader level, the United States and the Soviet Union can never agree completely on precisely what is military parity.

Their weapons are not identical. More significantly, they have different geographies, different military strategies, different histories and suspicions, and above all, different world objectives -- and enemies. While the United States currently sees itself as having only one nuclear adversary, the Soviet Union, the Kremlin counts four nuclear-armed opponents, even though three have small nuclear arsenals: the United States, Great Britain, France and China.

The unratified SALT II treaty does represent "parity" or "essential equivalence," the Carter administration has insisted; critics charged that it actually confirmed "Soviet superiority" or "looming Soviet superiority."

Although the agreement is in a state of limbo, the Carter administration has said that the United States will honor its terms, as long as the Soviet Union also does so.

While the Soviet Union has not made a parallel declaration, Secretary of State Edmund S. Muskie has said, "they have practiced that," treating it "as on option that is useful for them to reserve." The Soviet position is that it will discuss the treaty with the Reagan administration, but that it sees no reason to revise it. The passage of time, however, is affecting some of the limitations in the accord.

Although the treaty was intended to last until the end of 1985, it contains intermediate deadlines which run out this year.

Under its terms, the Soviet Union is required to reduce its total number of intercontinental missiles and bombers by about 270 at the end of this year, in order to comply with the agreed ceiling of 2,250 nuclear delivery vehicles for each nation by Dec. 31, 1981. The United States, which had approximately 2,060 strategic missiles and bombers when the treaty was signed in 1979, is allowed to increase its forces to the 2,250 level.

Another deadline that expires on Dec. 31, 1981, is in a protocol to the treaty, limiting the deployment of ground-launched and sea-launched cruise missiles in which the United States holds a significant lead.

Whether the SALT II treaty is salvaged or jettisoned, its fate will directly affect another set of negotiations: on nuclear weapons of shorter range, 1,200 to 1,500 miles, based in Europe.

After the SALT II agreement was signed by Carter and Soviet President Leonid Brezhnev in June 1979, NATO agreed to install 572 American medium-range Pershing II missiles and cruise missiles in Western Europe. They would replace older, shorter-range weapons, when the new missiles are ready for deployment. But it remains to be seen which nations will agree to accept the missiles on their territory. That decision, announced in December 1979 by NATO, was tied to an agreement to negotiate reductions on missiles based in Europe in the context of an anticipated SALT III pact.

The entire scenario is now shrouded in uncertainty. The Soviet Union was furious when it recognized, following the signing of the SALT II accord, that the United States was proceeding to commit new missiles to Western Europe, with range enough to reach the Soviet Union. Launced from Western Europe, the missiles would require only six minutes flight time to reach Soviet territory. Soviet missiles of comparable range of course could only reach targets in Western Europe, not the United States.

Soviet Defense Minister Dmitri Ustinov charged that it was an attempt "to change . . . the strategic situation in NATO's favor," altering the American-Soviet balance by "building up the power of American strategic nuclear forces" in the guise of "modernizing" NATO's European forces. The Soviet position is that any U.S. weapons "targeted on the Soviet Union -- no matter where they are stationed, in the United States or in Western Europe or in Asia," represent the same threat to Soviet interests.

To the West, the new Pershing missiles and cruise missiles, which are intended to be deployed starting in 1983, represent no shift in the strategic balance. Instead, they are seen as overdue responses to advanced Soviet SS20 missiles and Backfire bombers for use against targets in Western Europe, which can give the Soviet Union "nuclear preponderance in the European theatre."

It was primarily for the same reason -- to eliminate what might be seen by the Soviet Union as American vulnerability or weakness -- that the Carter administration agreed to deploy the massive projected system of MX (missile experimental) intercontinental missiles. Critics of the Carter administration's strategy insisted that it was not merely a matter of apparent weakness, but that the United States was dangerously exposed to a "first strike" from the improved destruction capacity of the Soviet missile force, which would wipe out America's entire force of land-based Minuteman missiles.

That would be an irrational, suicidal attack, which would leave the Soviet Union exposed to destruction from U.S. submarine-launced missiles and bomber-launched nuclear weapons, Carter administration officials maintain. It was the original premise of the "triad" of American air, sea and land forces that a loss of strength in "any leg" of the triad would be overcome by the strength of the other forces. But in a nuclear age in which weapons are targeted primarily on the mind, what is believed to exist acquires its own dynamic volatility.

The largest of several new weapons systems intended to overcome that image of American vulnerability is the controversial MX system, with 200 mobile missiles and 2,000 highly accurate warheads. With the capacity to fire from sites difficult to detect and to destroy Soviet missiles in their underground silos, the projected system would cost $33 billion by U.S. Air Force estimates -- and more than $100 billion according to critics. Reagan has questioned the intended basing mode for the system, which would stretch over 8,500 square miles of desert land in Nevada and Utah under current planning. One alternative proposed by a Reagan transition team is converting Minuteman III missiles into mobile weapons.

Ironically, the United States offered to forgo development of the MX system in the Carter administration's first nuclear arms proposal which the Soviet Union rejected peremptorily in March 1977. At that time, national security adviser Brzezinski said the Soviet Union should recognize that the MX system "could be extremely, extremely [sic] threatening to them," with "first-strike capability against their land-based systems."

Without some kind of ceiling on rival nuclear stockpiles, such as SALT II, however, the strategic rationale for the MX system would be greatly weakened. In the absence of any limits on Soviet force levels, the Soviet Union could add more missiles and warheads to overwhelm the MX force. That would involve huge costs, but the Soviet Unionl insists it would follow that road, whatever the expense to its economy.

The "mad nuclear mathematics" of American-Soviet rivalry make total Soviet nuclear forces far more vulnerable to attack from an MX-type system than the United States.

For while the United States has only 24 percent of its total nuclear strategic force based on land, 50 percent at sea, and the remainder aboard bombers, the Soviet Union has 70 percent of its strategic power in land-based missiles. The Soviet Union, therefore, would be theoretically vulnerable to the loss of three-quarters of its entire strategic force by American attack, while, in theory, the bulk of American forces would survive at sea or on bombers.

No American or Soviet leader is likely to risk the fate of his nation on such war-game calculations. But each is highly dependent on the rationality of the adversary for national survival; and both are vulnerable to their equally frail ability to calculate the opponent's intentions.

Each nation often genuinely sees itself as the victim of the other's unwarranted actions; but the Soviet Union never concedes error, misdeeds or provocation.

The Soviet Union charges that it is the White House and the Pentagon, not the Kremlin, which are attempting to overturn the strategic balance and achieve "military superiority." It accuses the United States of embarking on "a new Cold War," by creating "war hysteria," engaging in "feverish military preparations," concocting "pretexts" for its actions by accusations against the Soviet Union in Afghanistan and elsewhere, and no means least of all, colluding with China in "a dangerous new phenomenon in world politics."

This is, however, a politically sensitive time in the Soviet Union as well as in the United States, for the 26th Communist Party Congress in February is intended as a capstone on Brezhnev's career. The development of East-West detente is credited as Brezhnev's major accomplishment for peace and the advancement of Soviet interests.

But the nation's economic plan for 1981-85 offers only modest economic gains, and acknowledges shortcomings in output with more openness than customary. And with great uncertainties for East-West detente imbedded in the continuing tension in Poland, as well as in American-Soviet relations, this is not the most auspicious time for hailing detente.

The Soviet Union may well be interested in a respite in U.S.-Soviet tension, but not at the price of what it sees as its security interests, as Afghanistan demonstrated and as the forces prepared to enter Poland, if necessary, again illustrate.

Reagan expressed the belief during his campaign that if confronted with the challenge of an open-ended arms race, the Soviet Union would be obliged to come to terms on limiting the use of its global military power, as the price for an arms control pact. The Soviet Union is hardly likely to be responsive to such a frontal demand. If the experts are right about the timetable for acquiring knowledge in Moscow and Washington about how each side operates, the Reagan administration has about 18 months for its break-in period. But as the diplomats caution, that can also count the crash experience of a crisis.