Mikhail Gorbachev has announced his solution to the arms race: a mutual 50 percent reduction in offensive strategic weapons in return for an end to the Strategic Defense Initiative program. This 50 percent solution, designed to sound eminently reasonable to a variety of audiences, contains the potential for both breakthrough and breakdown.

The flaws contained in the proposal are apparent. The effects are heavily weighted in the Soviet Union's favor. It should be noted, however, that it is not unprecedented to find a party to a negotiation placing a heavy hand on its side of the scales. It is important to bear in mind that we are witnessing the dance of diplomacy, not the pouring of concrete. This is the beginning of the process and not th end product.

We believe President Reagan should respond to Gorbachev's proposal with something that is positive, strategically sound and politically sustainable. This last requirement should not be underestimated, for the Soviets have at least three major objectives in mind: 1)to stop "Star Wars" research; 2)to divide the NATO alliance, and 3)to undermine future congressional and public support for the president's strategic modernization and defense programs. It is unlikely that the Soviets can achieve their first goal, but if they can paint Reagan as being inflexible and uncompromising, then they may be able to win in Western Europe and indirectly in Congress what they could not achieve in Geneva.

Reports abound that guerrilla warfare is being waged within the administration between those who see no benefit in dealing with the Soviets except on our terms and those who see advantage in reaching a compromise. This battle should not be fought or concluded without a wary eye being cast on Capitol Hill. Congressional support for strategic modernization and defense programs has been predicated upon good-faith efforts to achieve dramatic reductions in offensive nuclear weapons. It would be a mistake, therefore, to focus only on the negative aspects of the Soviet proposal without attempting through serious negotiations to set the scales back in balance.

A sober analysis of the Soviet proposal should reveal that there are grounds for progress beyond the obvious one-sided advantages. The Soviets have dropped their unacceptable preconditions for discussing offensive reductions, and for the first time have proposed a specific numerical ceiling on nuclear warheads, a longtime U.S. objective. Moreover, their proposal would require substantial (though still insufficient) reductions in their destabilizing force of MIRVed ICBMs.

But other elements of the proposal are clearly unacceptable and prejudicial to Western security interests, such as the exemption from the proposal of all Soviet systems targeted on Europe. It remains now for the president to applaud the positive principles and seek to convert the negative components and tactics into an equitable agreement.

To accomplish this, the president must invite the Soviets to join him in searching for a mutually acceptable formula for achieving stability. For example, he should refocus attention upon a critical element underplayed in the Soviet proposal: the need for strong incentives to reduce the number of land-based, MIRVed missiles well below the levels permitted under the Soviet proposal. It is the high ratio of these vulnerable, counterforce weapons to their assigned targets that causes a tightening of the finger on the nuclear trigger. Both countries seem to be moving dangerously close to a launch-on-warning strategy -- the firing of the most accurate, destructive and vulnerable weapons upon the first warning that they are about to be attacked.

There are a number of ways to move toward greater stability. One approach, which we called the build-down, was adopted by the president in 1983 with broad congressional backing. Among its elements:

*An immediate cap on the number of nuclear warheads;

*Reductions in warheads through a requirement that deployment of new nuclear warheads be accompanied by elimination of a greater number of existing warheads;

*A similar reduction in bombers;

*Formulas aimed at channeling modernization in stabilizing directions such as mobility and single-warhead missiles;

*Negotiation of trade-offs between bomber payload and missile throw-weight.

Unfortunately, this proposal fell victim to insufficient development by the administration in discussions with the Soviets and to the Soviet walkout from Geneva in 1983. But subsequent events, including informal Soviet commentary and the present Gorbachev proposal, indicate a compatibility with key principles of the 1983 proposal, although there are differences over the specific formulations.

A key new ingredient, however, has been added since the 1983 Geneva talks: strategic defensive weapon systems. The administration argues that SDI was a major reason for the Soviet decision to return to the negotiating table. Yet in his recent press conference, the president appeared to rule out the possibility of negotiating any restrictions on the development and testing of ''Star Wars" until we know whether these weapons are feasible -- in short, several years from now. This position, if true, makes any progress in Geneva very unlikely. And a stalemate in Geneva would offer the Soviets a means of furthering their objectives in undermining domestic and Allied support for needed modernization programs.

The United States can propel the negotiations forward by adopting an approach that addresses SDI and is consistent with our objectives and programs.

While maintaining a reasonably funded research program, we should discuss with the Soviets what constitutes allowable development and testing under the provisions of the ABM Treaty. In the two years since the president's original "Star Wars" speech, the Soviets have come up with interpretations of key treaty limits that are far more restrictive than what we agreed to in 1972. Over the same period, the administration has been formulating increasingly permissive interpretations of the relevant treaty provisions to allow as much of the SDI to go forward as possible. A reasonable middle ground would be for both sides to agree to live with the restrictions on development and testing that were mutually accepted at the time the treaty was signed. This is, after all, the legal obligation of both parties.

We should inform the Soviets that we are prepared to reexamine the scope and pace of a possible transition to increased reliance on strategic defenses if they are prepared to do thre things: agree to meaningful and stabilizing reductions in strategic and intermediate- range nuclear forces, satisfy U.S. concerns regarding current violations of existing strategic arms control agreements (including the construction of the radar at Krasnoyarsk), and work with us in identifying realistic and verifiable breakpoints between research and development beyond which their SDI and ours would not be allowed to progress.

It is not necessary for the president to reach an accord with Gorbachev to preserve congressional support for his programs. But a Reagan "nyet" is not enough. If a budget-conscious Congress perceives that opportunities for an accord were deliberately ignored or sabotaged, then it is unlikely to retain enthusiasm for those programs high on the president's agenda. Good faith could become a line item -- one the president has the power to veto.