PRESIDENT REAGAN stood at the podium in the White House press room, smiling. Next to him, also smiling, stood Soviet Foreign Minister Eduard Shevardnadze. Reading from his customary index card, the President announced a December superpower summit in Washington, where in all likelihood a treaty eliminating intermediate-range nuclear weapons will be signed. Then he said he had time for only a few questions, as the gentlemen with him had not yet had lunch.
Once this would have been thought an improbable, if not impossible, scene: Ronald Reagan, the man who called the Soviet Union an evil empire, boasting of a pending arms control agreement. But on Oct. 30 it happened, and in a few weeks, Soviet leader Mikhail Gorbachev is expected to land in the United States to consummate the first US-Soviet arms treaty in eight years.
Although the military significance of the intermediate-range (INF) pact is unclear, the treaty signals a turning point in superpower relations. If this President, the most rhetorically conservative of the postwar era, inks a deal with the Soviets, the voting public will likely expect any future chief executive to pursue arms control.
But in some respects, the INF deal is already old news. In the halls of government and Washington think tanks, experts are looking beyond INF and focusing on two questions:
What, if anything, should NATO do to bolster its forces in Europe after US intermediate-range missiles are withdrawn? Options range from more tanks to a new short-range nuclear weapon.
Should the US agree to negotiate limits on tests of the Strategic Defense Initiative? President Reagan adamantly says no, but General Secretary Gorbachev says that without such limits there can be no progress in the main arms control arena, talks on long-range nuclear weapons. NO matter what happens next, it seems clear that Ronald Reagan's attitudes toward the Soviet Union have changed a great deal.
As a candidate and in the early years of his presidency, Mr. Reagan spoke harshly of the Soviets. Previous Presidents, he said, had been too soft in superpower negotiations and too willing to ignore Soviet cheating on existing arms pacts. In his first press conference as President he said the Soviets ``reserve unto themselves the right to commit any crime, to lie, to cheat.'' In a 1982 European tour Reagan called for a ``crusade'' against Soviet communism, and called the USSR ``the focus of evil in the modern world.''
By contrast, in a speech last month at the US Military Academy at West Point, N.Y., Reagan sounded downright friendly. He called the Soviet Union ``democracy's main competitor'' instead of an evil empire and said that in some areas US-Soviet relations had shown ``positive developments.''
In some ways this softening position is more stylistic than substantive. The basic US position in the INF talks has changed little over five years - and eventually the Soviets accepted it. But in the difficult game of power diplomacy, where leaders grope to understand each other's intentions, less hostile rhetoric can do much to relax tensions.
One measure of how far Reagan has moved is his standing among staunch conservatives, the bedrock of his political support. Many have broken with the White House over INF. Some Republican senators, citing concerns about the treaty's verification provisions, are threatening to fight hard against Senate ratification. Of GOP presidential candidates, only Vice-President George Bush says he supports the pact.
``It's ridiculous to contemplate a new arms agreement with the Soviets when they are still violating the old ones,'' said James Hackett, an analyst with the Heritage Foundation, in the wake of the treaty announcement.
The leadership of the Soviet Union, for its part, has changed significantly since 1980. The drift of the Brezhnev era has been replaced by the dynamism of Mr. Gorbachev's glasnost. Arms proposals - from a nuclear testing ban to elimination of all nuclear weapons - have flowed from the Soviet Union so fast that US officials have often felt at a propaganda disadvantage.
The President, in his West Point speech, acknowledged that change for the good is taking place inside the Soviet Union - particularly in human rights. Some Soviet political prisoners have been released, and there has been a rise in the number of dissidents allowed to emigrate. But Reagan reprimanded the Soviets for their continued military presence in Afghanistan and for meddling in other regional conflicts.
In private, some US officials add that recent Soviet behavior has left them puzzled. First, Gorbachev indicated he would not come to the US to sign an INF treaty; then, a few days later, he changed his mind. After that, on the 70th anniversary of the Bolshevik Revolution, he gave a speech that was more hard line than expected. For these and other reasons, at least one knowledgeable US official says he is more confused about US-Soviet relations than at any other time during the Reagan presidency.
AGAINST this background, officials all over Washington are beginning to examine what the superpower military balance will look like after INF missiles are destroyed. In particular, they are looking at ways to make sure that the deterrence value of NATO forces in central Europe is not diminished by the loss of Pershing 2 and Tomahawk missiles.
The US and its allies see the impending INF pact ``as a cause for celebration, and then a cause for a pause'' to evaluate the future of the military alliance, says Alton Keel, US representative to NATO. US officials say an INF pact will be of military benefit to the West, because the Soviets will destroy more warheads than the US will - 1,591 to 348. But they also worry that with the removal of these nuclear forces from superpower arsenals, conventional weapons - tanks, artillery, small arms - will become more important to the balance of power in Central Europe.
By many measures, the Warsaw Pact has stronger conventional armies than NATO does. Some Western planners worry that while an INF treaty could lessen the chance of nuclear holocaust in Europe, it might paradoxically increase the chances of a conventional World War III.
One answer to this perceived problem would be to increase spending on conventional arms. Most experts considered this unlikely even before the worldwide slide in stock prices began making many Western leaders anxious about their economies.
Another response would be to modernize and perhaps add to types of nuclear forces not covered by the INF pact. NATO defense ministers met in Monterey, Calif., earlier this month to consider just such a move.
Among the new nuclear weapons discussed was an upgrading of the aging Lance surface-to-surface missile, which with a range of only 74 miles does not qualify as an intermediate-range weapon. The defense ministers also discussed adding to the number of submarine-launched missiles and nuclear-capable aircraft earmarked for NATO purposes and possible deployment of a new type of air-launched nuclear cruise missile.
US officials are sensitive about the implication that they are looking for ways to get around the limits of an INF pact. NATO representative Keel says there will not be a one-to-one replacement of banned INF warheads with new weapons not covered by a treaty. ``There will be a net reduction'' in nuclear weapons in Europe as a result of an INF agreement, he says.
Western officials say that one thing that concerns them about the impending INF pact is that Gorbachev will use it as a springboard to continue to press for removal of all nuclear weapons from Europe - a move they feel would greatly weaken Western security.
Soviet diplomats are pushing to include short-range, so-called ``battlefield'' nuclear weapons in the longstanding talks on conventional arms reductions being held in Vienna, according to Charles Thomas, a US representative to NATO for conventional arms control. But US diplomats are insisting that reductions in tanks must be nailed down before moving to short-range nuclear systems, Mr. Thomas told the Senate Armed Services Committee early this month.
The US would prefer that the arms control process now focus on obtaining a 50 percent reduction in long-range strategic weapons - the intercontinental missiles and bombers that are the heart of superpower nuclear arsenals. Indeed, US officials say a surprising amount of progress has been made in the START talks in recent months.
US and Soviet negotiators in Geneva are working in a businesslike atmosphere on a draft document describing areas of agreement and disagreement on strategic arms. The Soviets are discussing sublimits on particular types of nuclear missiles, a topic they had previously been reluctant to address.
But a giant obstacle to a historic strategic pact remains: differences over the US Strategic Defense Initiative.
The USSR is proposing to negotiate what sorts of SDI tests will be allowed under the 1972 Antiballistic Missile Treaty, which is somewhat vague on the subject. Soviet negotiators have submitted a list of proposed specific limits on brightness of lasers, speed of interceptor rockets, and other measures of SDI technology.
Some US officials, notably Paul Nitze, a special presidential arms control adviser, favor talking with the Soviets about such limits. They feel that by agreeing to a slowdown in SDI development the US can eventually have both the option of deploying defenses and a big cut in the most dangerous weapons on earth.
But the official US position - backed by President Reagan and hard-liners in the Pentagon - is that talking about restraints is just the Soviet way of attempting to kill the program and that there will be no negotiating over SDI.
US-Soviet relations are in ferment, perhaps more so than at any time since the beginning of the period of d'etente in the late 1960s. The challenge for the next president, US officials say, will be to try to improve relations with a dynamic Soviet leader while retaining a healthy skepticism about Soviet motives.
``There is little chance of extreme trust developing between us. But we must do business,'' says Dr. Alan Mense, acting SDI chief scientist. CHARTS: 1) Major steps in arms control. 1963 Limited Test Ban Treaty prohibits all nuclear tests aboveground, underwater, or in space. Underground explosions that release radioactive debris beyond the nation's borders also banned. 1972 SALT I accords signed by President Nixon and Soviet leader Brezhnev. Interim agreement on strategic offensive arms freezes the levels of some offensive weapons. Antiballistic Missile (ABM) Treaty limits development of defensive missile systems. 1974 US-Soviet Threshold Test Ban Treaty limits size of underground nuclear weapon tests. 1979 President Carter and Soviet leader Brezhnev sign SALT II Treaty, limiting some categories of strategic offensive weapons. Agreement was never ratified. NATO agrees to deploy new INF forces (US Pershing 2 and cruise missiles) in Western Europe to counter a Soviet buildup of SS-20 rockets. 1981 INF talks begin in Geneva. President Reagan pledges to cancel deployment of Pershing 2s if Soviets dismantle SS-20s, but rejects Soviet plan that would permit some SS-20s but no US INF missiles in Europe. 1982 Separate talks on cutting long-range strategic nuclear weapons, dubbed START, begin in Geneva. 1983 President Reagan announces Strategic Defense Initiative program to research a space-based missile defense system. Deployment of cruise and Pershing 2 missiles in Europe begins. Soviet Union walks out of INF talks and refuses to continue START talks. 1985 Superpowers resume INF and START talks, adding ``star wars'' to the agenda. Reagan and Gorbachev hold summit meeting in Geneva in November, but reach no arms control agreements. 1986 Reagan and Gorbachev, meeting in Reykjavik, Iceland, come close to a sweeping arms control deal, including cutting INF missiles to 100 each with none in Europe, and drastic cuts in long-range forces. But Gorbachev insists on limits on SDI as well and talks collapse. 1987 In July, Gorbachev says Soviets will accept INF proposal, eliminating all INF missiles, but says West Germany's Pershing 1A missiles (with US-controlled warheads) must be included. In August, West German Chancellor Helmut Kohl removes a major remaining obstacle to an INF pact, agreeing conditionally to dismantle the 72 Pershing 1A missiles. 2) Assessing the NATO-Warsaw Pact balance Manpower The Warsaw Pact has about 50 percent more ground force troops in Europe than NATO does. But the numbers (2.7 million to 1.8 million) don't tell the whole story. NATO forces train harder and are thought to have superior leadership. Some 800,000 of the Warsaw Pact soldiers are Eastern Europeans whose loyalty could be questionable in a major conflict. Tanks Warsaw Pact tanks outnumber NATO's, 46,600 to 20,300. Many Pact tanks are venerable T-54s and T-55s, and top-of-the-line Western tanks are thought to be more than a match for the best Soviet models. But the vast tank imbalance remains a concern. Aircraft The capabilities of the best NATO warplanes (US F-15s, British and German Tornados, and others) are much greater than those of their Warsaw Pact counterparts. The Pact has more bombers, fighters, and ground-attack jets than NATO (3,500 to 2,800), but Western commanders talk confidently of dominating the skies of Central Europe. Short-range (tactical) nuclear weapons Even if medium-range missiles are excluded, the Warsaw Pact has more tactical nuclear weapons than does the West. The USSR and its allies have about 291 short-range Scud and Frog missiles, for example, while NATO fields 163 short-range Lances. The Warsaw Pact is vastly superior in the number of artillery pieces capable of firing nuclear shells. Many of NATO's superior aircraft can carry nuclear bombs, and some 400 US submarine-launched Poseidon missiles are thought to be assigned to NATO.