US arms reduction plan: 'a good first step,' but

President Reagan's strategic arms control proposal is receiving thoughtful attention from experts across the political and philosophical spectrum.

Despite Soviet President Leonid I. Brezhnev's apparent rejection of Mr. Reagan's proposal, Secretary of State Alexander M. Haig Jr. may meet with Soviet Foreign Minister Andrei A. Gromyko in New York next month to begin discussions. NATO foreign ministers meeting this week in Luxembourg have welcomed Mr. Reagan's plan for sharply reducing the nuclear arsenals of the two superpowers.

In general, the plan is viewed by analysts and advocates here as a good first step. But many also are finding the administration's arms control gambit lacking in several important areas.

For example, some find it so structured that the key goal -- stability - could be reduced, even though total stockpiles would be cut significantly.

''The problem is that not all reductions are benign, and not all forms of parity lead to stability,'' observes Rep. Albert Gore Jr. (D) of Tennessee. ''It is quite possible to realign the forces of both countries in conformity with the President's proposal, in a way that would lead not to greater stability but to less stability.''

Here, Representative Gore, who has offered his own arms control proposal, which has received wide attention, was referring to the arming of land-based missiles with multiple warheads, which is not specifically addressed in Reagan's plan.

The first phase of the President's proposal would reduce each side's arsenal of land -- and sea-based ballistic missiles to 850, with a total of 5,000 ballistic missile warheads and no more than 2,500 of these to be based on land.

The second phase of the administration plan would reduce total missile throw weight -- the amount of payload weight a missile can carry -- to less than the current US level. Bombers and cruise missiles are not mentioned in the proposal, but the President has said ''nothing is excluded'' when negotiations begin.

The aim is to reduce the current Soviet advantage in heavy, very accurate land-based missiles, a counter-force capability that officials say makes America's ICBMS dangerously vulnerable to a first strike.

This may be true, argues Arms Control Association president Herbert Scoville, but ''any US ICBM 'window of vulneraility' will have been opened wider by the new START proposal.''

In recent Senate testimony and in a meeting with reporters this week, Dr. Scoville (who has been active in government and private arms reductions efforts for many years) commended the administration for making a serious arms reduction proposal.

But he also detailed how the nuclear arms balance could become more dangerous if the Reagam plan were adopted without change.

For example, if the US were to deploy 200 MX missiles and 12 Trident submarines with Trident II missiles, it would be just within the proposed 5,000 -warhead limit for ballistic missile warheads. Because the Soviet Union would still be allowed 2,500 ICBM warheads, this could increase the number of highly accurate Soviet weapons per US missile silo by as much as three times.

At the same time, according to this scenario, the number of allowable US strategic submarines would be reduced making US subs less survivable.

Soviet first-strike vulnerability likewise would increase, says Dr. Scoville, particularly if the Soviet Union chose to keep the heavy SS-18 ICBMs that currently can carry 10 warheads each.

Since each side would be pressing forward with its modern missiles under this scenario, while at the same time becoming relatively more vulnerable, the chances of a first strike being launched are increased.

''The security of both countries would be improved if there were also restrictions on the number of MIRVed (multiple warhead) missiles allowed within the quotas, particularly those with large numbers of warheads,'' says Dr. Scoville.

A lengthy and detailed report on nuclear strategy just released by the Carnegie Endowment for International Peace acknowledges the growing (and dangerous) vulnerability of US ICBMs. But it maintains (as does James Schlesinger, secretary of defense in the Nixon administration) that even without its ICBMs, the US possesses sufficient nuclear weaponry ''to perform the assured destruction mission.''

''Reductions . . . could improve the survivability of our forces if properly structured,'' states the Carnegie Endowment report. ''However, the more 'negotiable' approaches such as across-the-board reductions . . . could, depending on how they are implemented, increase vulnerability and reduce crisis stability.''

It may seem ironic that strategic weapons reductions -- depending on how they are affected -- could in fact mean a more dangerous world. But that is just one indication of how difficult it may be to achieve effective arms control and why it is likely to take so long.