Paul H. Nitze, former deputy secretary of defense and a leading opponent of the proposed strategic arms limitation treaty (SALT), charged yesterday that U.S. negotiators are "avoiding the most important issue" with the Soviet Union, a "shell game" missile deployment system.

In a press conference sponsored by the Committee on the Present Danger, of which he is chairman of policy studies, Nitze said the United States has been unable to obtain a clear understanding with the Soviets about the legitimacy of such a deployment scheme under the SALT II treaty.

Under the "shell game" plan, which Nitze has long espoused, the United States would secretly rotate a limited number of mobile intercontinental nuclear missiles among a larger group of possible launching points. The idea is to confound Soviet gunners in the 1980s, when U.S. land-based missiles will be increasingly vulnerable to a massive strike by increasingly accurate Soviet missiles.

The proposed system, which is under study in several variants in the Defense Department, was mentioned to the Soviets as a U.S. option for the future during a SALT meeting in Geneva in July. The Soviets reportedly objected to it on the grounds it could not be verified under SALT rules.

On Aug. 22, Secretary of Defense Harold Brown officially stated that any future U.S. mobile missile system will be "fully consistent" with verification, and that the United States will be permitted to build such a verifiable system under SALT II. He also said no decision has been made whether or not to do so.

Nitze dismissed as a matter of "cosmetics" without much substance the still unresolved issue of Soviet encoding of some missile test information which is electronically transmitted back to earth. This is reported to be the major hurdle to a new SALT agreement.

The former defense official said his "suspicion" is that the United States in the past has encoded its electronic test data, or telemetry. He also said "we've put things into capsules and then dropped the capsules" to avoid disclosure of telemetry information.

Nitze said he believes it is impractical to write a SALT provision which would require the Soviet Union to reveal to the United States its important test data.