The Soviet Union could deploy hundreds of long-range missiles overnight by violating "an utterly unverifiable" provision of the proposed SALT II pact, former Defense Intelligence Agency official Daniel O. Graham said yesterday.

An article of the strategic arms limitation treaty prohibits the Soviets from producing, testing or deploying any SS16 single-warhead, intercontinental ballistic missile. But Graham said the SS16 might be produced covertly in factories and fired from launchers on hugh trucks -- launchers that do not count against treaty limits.

The mobile launchers now are intended for use with an intermediate-range missile, the SS20. Graham said the SS20 could be converted into a long-range SS16 merely by adding a warhead. Production of that warhead in Soviet factories would be unverifiable, he said.

Graham said the Soviet Union already has 200 mobile launchers, which can fire missiles from any hard surface. These, he said, could pick up missiles and deploy them "in one night's time."

A vocal critic of SALT II, Graham spoke at a press conference sponsored by the American Security Council, a private lobbying group that favors a more forceful national defense posture. He said he waited until yesterday to publicize the SS16 problem, which he said is "of crucial importance," because "I felt someone would bore in on it" during the congressional hearings on the treaty earlier this summer.

Whether the Soviets would actually deploy the SS16s as Graham suggests is "a technically interesting issue, but one you'd have to really stretch your mind on to see why they'd want to," countered Spurgeon M. Keeney Jr., deputy director of the Arms Control and Disarmament Agency.

"For one thing, they'd have to rely on a weapon they have not tested thoroughly," he said. And, to substitute SS16s for SS20s on the mobile launchers, "they'd have to pull out their first-line forces against NATO," he added.

"Only a madman would ignore the rest of the world, where our forces, not to mention our allies', are," he claimed.

Keeney also argued that a complete ban on production of SS16s offers "a number of possibilities for monitoring for compliance.".

Verification of Soviet compliance with the terms of SALT II has been a major focus of questioning of the treaty. But, while some senators are still concerned with verification, others have been reassured by CIA Director Stansfield Turner's firm support of the treaty's verifiability. Sen. Barry Goldwater (R-Ariz.) has stated publicly that he thinks the verification problems are manageable.