Panel says greater flexibility on part of both superpowers is key to new arms-control pact

An independent panel of experts concludes that prospects for US-Soviet agreements on the control of nuclear weapons are bleak unless there is ''considerable compromise'' on the American side.

On the bright side, however, the panel, organized by the Carnegie Endowment for International Peace, asserts that a combination of internal economic pressures and the threat of new generations of American weapons may induce the Soviets to accept modest limitations and reductions.

The 30-member panel, which has been meeting periodically for the past three years, concludes as well that despite apparent stagnation in both the Strategic Arms Reduction Talks (START) and Intermediate-range Nuclear Forces (INF) negotiations, the arms-control process is still viable. In support of this, it argues that both sides' proposals reflect continuity with the past, though it also recognizes the need for more radical measures. Both the Soviets and Americans have shown a willingness to abide by several unratified or expired treaties.

The Carnegie panel, established in 1980, was cochaired by William G. Hyland, senior associate at the Carnegie Endowment and a former deputy assistant for national security affairs to President Ford, and Joseph S. Nye Jr., professor of government at Harvard University and a former deputy to the undersecretary of state in the Carter administration. The panel's 101-page report, entitled ''Challenges for US National Security,'' in effect urges the Reagan administration to move away from what its members describe as ''unrealistic hopes of forcing radical reductions in, and restructuring of, Soviet forces.''

At Eureka College nearly a year ago, President Reagan proposed sharp reductions in long-range missiles and nuclear warheads. The President suggested that the Soviet Union give up many of its large land-based missiles by accepting a limit of 5,000 missile warheads on no more than about 850 missile launchers. He said little about curbing American advantages in submarines, cruise missiles, and long-range bombers, but also did not exclude negotiations over those weapons systems.

The Soviet Union has concentrated the largest part of its strategic nuclear forces in land-based missiles, while the US has invested only about one-quarter of its megatonnage in land-based ICBMs. The Carnegie panel asserts that it is unrealistic to expect the Soviets to accept sharp cuts in the force in which it has invested the most. Panel members argue that this is in part because of the Soviets' bent for bureaucratically complex, long-range planning, which limits their flexibility.

The Carnegie panel says that the current Soviet proposals at the START negotiations are not any more likely to lead to an agreement than are the Reagan proposals. Each side has so far aimed its proposals at the other's strengths. Indeed, the Soviets' position requires the Americans to make more unilateral changes in weapons planning than the Reagan proposal would require of the Soviets. The Soviets propose, among other things, blocking several new American weapons systems which are not yet ''operational.''

The panel thus seems to be urging both sides to adopt a more pragmatic, step-by-step approach. Unlike proponents of a total nuclear freeze, panel members do not oppose some technological development or strategic force ''modernization,'' if it has the effect of reducing the incentive for a surprise attack and creating greater stability in a crisis. Panel members were divided over the Reagan administration plan to deploy 100 MX missiles in existing missile silos, but some of them saw virtue in use of the MX as a bargaining chip to induce Soviet concessions.

Panel members also saw some signs of pragmatism in the Reagan administration approach to the theory of ''linkage.'' When President Reagan first took power, he indicated that arms-control talks with the Soviets (and a summit meeting) could not begin until the Soviets moderated their behavior in third-world nations, such as El Salvador. Now the Reagan administration seems to accept, perhaps because of pressure from both the American and West European publics, that arms-control negotiations may be worth pursuing for their own sake and need not be explicitly linked to other developments.

The Carnegie report is coming at a time when the Reagan administration is showing other signs of pragmatism. The signs could be seen in these Reagan decisions: (1) to hold off charging the Soviets with SALT II violations until further study can be done on the issue, (2) to offer a long-term grain sales agreement to the Soviets, and (3) to modify insistence on restricting West Europe's trade with the Soviet Union in the interest of holding a harmonious summit meeting of the industrialized democracies at the end of May.

The Carnegie panel lists several factors that could improve the climate for strategic arms control. One is what the panel describes as a rise in public support for arms control in the US. A second factor is the economic predicaments of both the USSR and the US. Finally, says the panel, arms control may benefit from a perception on the part of the Soviets that with the Reagan administration's defense buildup, the military equilibrium could shift in favor of the US.

The panel says the Soviets may have four options:

* If the Soviets calculate that they can enhance their strategic position at relatively little risk and cost, they may use arms control as a safety valve.

* The Soviets could simply retrench and consolidate, using arms control to buy time and limit the damage they might otherwise sustain in an all-out arms race.

* The Soviets could calculate that they are up against an American adversary that is bent on weakening their position and even ultimately destroying them. A more flexible approach to arms control, they might calculate, would only embolden the US.

* The Soviets might simply be unable to formulate and gain internal approval for any coherent arms control strategy and thus only be able to proceed with their current weapons programs.