As the world enters the 39th year of the nuclear age, the United States and the Soviet Union are poised on the edge of major developments in thermonuclear weapons and are searching for ways to prevent nuclear war.
Most analysts expect that the status quo will not continue: Either an accelerated arms race or real progress on disarmament will follow. As the President's Commission on Strategic Forces (the Scowcroft Commission) warned, ''Nuclear weapons have sharply raised the stakes and changed the nature of warfare.''
The issues are not abstract or theoretical. Nor are they simply military, political, or fiscal. At base, they are moral. Military chaplains these days are having to explain, debate, and take sides on the Roman Catholic bishops' pastoral letter on nuclear war.
If one looks at new weapons about to be deployed or nearing completion of development, the picture is not encouraging: intercontinental ballistic missiles (ICBMs) with precise, ''hard-target kill'' capability, hard-to-find cruise missiles, antisatellite weapons, rockets that can be used for conventional or nuclear attack, thus blurring the ''nuclear threshold,'' submarines and aircraft that are becoming more stealthy. Many arms control experts warn that these developments could undercut deterrence based on ''mutual assured destruction'' (MAD) - in which neither side attacks because each knows the other possesses sufficient forces to withstand a first strike and still inflict unacceptable damage on its attacker. Some say this has helped keep the nuclear peace since the first atomic bomb fell in 1945. MAD is weakened when nuclear weapons become sufficiently accurate to foster the perception of, if not actually provide, the ability to destroy most of an enemy's strategic forces in a first strike.
''Both sides seem bent on acquiring nuclear weapons with war-fighting capability, while the leaders of both sides purport to recognize that neither country could fight, survive, and win a nuclear war,'' SALT II negotiator Paul C. Warnke told the Senate Foreign Relations Committee this summer.
Meanwhile, the parallel race to achieve nuclear arsenal stability and to lower the nuclear threshold continues at a more tortoise-like pace. Despite some apparent flexibility on both sides, there have been no breakthroughs at Geneva - the site of the strategic arms reductions talks (START) and intermediate-range nuclear force (INF) negotiations. There is mounting evidence that the Soviets may be violating existing arms control agreements by testing and deploying new systems. This may have been what the US reconnaissance aircraft was checking on the night the South Korean airliner was shot down by a Soviet interceptor.
What experts see as the one successful arms treaty - which limits antiballistic missile systems - is threatened by new efforts to defend against nuclear attack.
And both sides have been posturing for political advantage as the December date for deployment of NATO Pershing II and ground-launched cruise missiles draws near.
The recent tragic episode with the South Korean passenger jet has not simplified the search for arms reductions, although arms control advocates say it makes the need to find an agreement even more urgent.
''I think it's all the more important that we do get some sort of agreement on both intermediate-range forces and strategic forces,'' says John Isaacs, legislative director of Council for a Livable World. ''The fact that Reagan is continuing the talks indicates to me that he may be more serious than I had previously thought on arms control.''
There are other hopeful signs as well. Over the summer months, a number of serious and thoughtful new ideas have been put forth to reduce superpower tensions and begin the necessary steps toward lasting disarmament.
Former US arms control negotiators Gerard Smith and Mr. Warnke next week are expected to offer proposals to reach initial agreements on INF and START, followed by comprehensive limits merging the two sets of talks.
There are new calls for more cooperative scientific research between the superpowers and a ''pacification of the global commons,'' including the oceans and space. In light of the ''transparency revolution'' that will ultimately make all weapons systems and their controlling facilities vulnerable, these efforts could reduce the chances of a ''hair trigger'' situation developing and help head off the drive toward spaced based weapons systems, reports Worldwatch Institute senior researcher Daniel Deudney.
Rep. Les Aspin (D) of Wisconsin has outlined ways he says the major sticking points on strategic nuclear weapons could be overcome. And there are other urgent calls from the political right as well as left to break the domestic political impasse on an issue that promises to be one of the 1984 presidential campaign's hottest. It is generally agreed that domestic consensus on nuclear weapons and how to reduce their threat is a prerequisite to any agreement with Moscow.
''We have got to, among ourselves, reach some compromise on these issues if we are to reach an agreement on arms control,'' says Richard Helms, former CIA director and now a member of the Scowcroft Commission. ''It's inconceivable that we could get either force modernization or arms control without bipartisan support.''
Thus, national security and nuclear arms, once the domain of technicians and tacticians, is an issue whose resolution ultimately will be framed by the public. This is already evident in the Reagan administration's new offers at Geneva, which are impelled in part by such indicators as the Business Week/Harris poll showing that 81 percent of those surveyed favor a mutual, verifiable US-Soviet nuclear freeze.
''There has in fact been substantial movement by the administration in its START proposal,'' Brent Scowcroft, chairman of the commission that bears his name, said recently. ''And the Soviets have made some positive steps.''
Before the last round of talks ended, the US eased up on its insistence that the USSR cut its lead in heavy, multiwarhead missiles by large amounts. Critics had said this was necessary in order to expect any positive Soviet response.
Reagan's decision to keep the Scowcroft Commission in operation also is in response to mounting public pressure for progress on nuclear disarmament. The commission, respected by many for its measured views and recommendations, will have put its stamp on the American proposal when START talks resume the week after next.
Chief US START negotiator Edward L. Rowny told reporters that President Reagan is sending him back to Geneva ''with a great deal of flexibility.''
Still, the US position on strategic and intermediate-range missiles remains essentially that ''peace must be built on strength,'' as President Reagan told an American Legion convention last month. The emphasis is on strength and an implied threat: If the Soviet Union fails to dismantle much of what it has, the US will build and put into the field its newest - but as yet undeployed - nuclear weapons. In fact, according to administration officials, such new US weapons as the MX and Trident II missiles and the B-1 bomber ought to be deployed in any case, since most US strategic forces are older than those in Moscow's arsenal.
And, despite recent hints at flexibility, the two sides remain quite far apart in their formal START positions.
''One can argue that fundamentally we are asking of the Soviets something which they are very unlikely to be able to do under any circumstances, which is to reconstruct their strategic forces,'' acknowledges one presidential arms control adviser.
For the moment, the South Korean airliner incident makes it more likely that Congress will approve money to build the first MX missiles and that the Senate will defeat the House-passed nuclear freeze resolution by an even wider margin than previously thought.
But those determined to push ahead with arms control are redoubling their efforts, too.
''I think these talks and what they hope to avert are too important to get mucked about in politics,'' says Barry Blechman, vice-president of the Roosevelt Center for American Policy Studies and former assistant director of the US Arms Control and Disarmament Agency (ACDA).
He and fellow former ACDA official Janne E. Nolan have recommended that the current arms control agency be abolished, that the secretary of state be directly responsible for implementing US arms control policy, and that the relatively obscure General Advisory Committee for Arms Control and Disarmament - a presidential commission with little authority - be made responsible to Congress as well as the president. Such steps, the two believe, would help depoliticize arms control and lead to more reasoned, bipartisan US positions and policy.
More immediately, arms control advocates have specific proposals of their own for reducing US and Soviet nuclear armament and stabilizing the ''balance of terror.''
The Committee for National Security, which Warnke chairs, has proposed a mutual ban on new land-based, multiple-warhead missiles, a 50 percent reduction in the SALT II ceiling on multiple-warhead missiles (from 1,200 to 600), a reduction in the total number of strategic nuclear-delivery vehicles from the SALT II ceiling of 2,250 to 1,650, and a moratorium on new sea-launched ballistic and cruise missiles.
''This approach would result in equivalent restraints and greater security on both sides,'' Warnke told senators recently.
Expanding on these ideas, Warnke and SALT I negotiator Gerard Smith next week are expected to send to General Scowcroft recommendations for strategic and intermediate-range nuclear force reductions.
Their INF plan initially would be along the lines of the so-called walk-in-the-woods formula worked out informally by the US and Soviet negotiators last year, but rejected by both countries. This would have canceled deployment of the Pershing II missile (which will be able to reach Soviet soil from West Germany in a matter of minutes) while permitting deployment of some slower ground-launched cruise missiles to match a reduced number of Soviet missiles of this range.
Smith and Warnke suggest canceling the Pershing II deployment and delaying the cruise missiles in return for a Soviet reduction to the pre-1977 level of 600 warheads worldwide on such missiles - less than half what it now has. Soviet President Yuri Andropov's recent offer to ''liquidate'' rather than simply relocate his country's intermediate-range missiles, including some of the newer SS-20s, now seems to make such an idea more realistic.
British and French strategic nuclear forces - now numbering 162 missiles, but scheduled to grow about eightfold in targetable warheads and therefore quite worrisome to Moscow - wouldn't be considered in this interim pact.
On START, Warnke and Smith are expected to recommend paralleling SALT II, but with lower sublimits on types of forces. This would result in significant reductions in the heavy, accurate, multiwarhead Soviet missiles in return for a US agreement not to deploy the MX or sea-launched cruise missiles. During the second phase of such reductions, the INF and START talks would be combined, and comprehensive launcher and warhead limits would be sought with some freedom to mix according to national needs and capabilities. At this point, some account might be taken of the British and French forces.
Increasingly, experts say the two sets of negotiations at Geneva must be merged if any agreement is to be reached.
''If you're really in search of an agreement, you could solve a lot of the problems by combining the talks,'' says Arms Control Association spokesman Thomas Longstreth.
The summer delay in arms control progress also makes it more likely that any agreement acceptable to an increasingly restive Congress (which is holding the MX hostage to such progress) has to include the ''build down'' notion advanced by Sens. Sam Nunn (D) of Georgia and William-Cohen (R) of Maine. This would require that any new strategic missiles (including the proposed ''Midgetman'' single-warhead ICBM) replace, and not simply be added to, existing missile forces, thus reducing overall numbers.
Recently, Wisconsin's Representative Aspin, a leading Capitol Hill expert on strategic forces, offered suggestions for compromise that Scowcroft said ''get to the heart of some of the most vexing problems on arms control.''
Aspin would seek substantial reductions in the large Soviet advantage on throw weight (how much destructive power and guidance equipment a missile can carry), but allow a more gradual evolution toward US-Soviet parity. He would look for ways to account for the relative advantages (accuracy) and disadvantages (slow speed) of bombers as well as for the larger US strategic aircraft arsenal. On heavy, multiple-warhead missiles (of which the Soviet Union has many more than the US), Aspin would search for incentives to move away from such destabilizing weapons rather than demand that they sharply reduce right away.
Such issues are extremely complex. Finding ways to verify any agreement will be even more difficult. What worries moderates like Aspin is that the hurdles in Washington may be just as high as the ones in Geneva.
''The goal is not to score a few points in a continuing policy debate,'' he says. ''The goal is to resolve the core disputes that divide the American polity into rival camps that stymie arms control.''
In the coming months and as the 1984 election approaches, finding this path to domestic compromise is likely to be the necessary first step toward advancing world peace.