Suspense is again building over whether the president will stick with SALT II. Before Ronald Reagan became president, this Carter-era treaty represented to him everything suspect about arms control, including its verification. Once in the White House, he found the unratified but informally observed treaty a useful check on Soviet arms-building. Still, alleged Soviet arms control violations have deeply troubled him and many others. His ambivalence was evident in a decision of June 1985. To encourage his own arms control talks at Geneva, he went against a strong conservative current and dismantled an old Poseidon submarine while putting a new Trident sub into service, thereby holding to his policy of not ratifying but not undercutting SALT II. However, he also announced a new policy of "proportionate response" to Soviet violations.

In the name of this policy, President Reagan is expected shortly to take certain compensating measures within the terms of SALT II. If he doesn't, people would ask what all the fuss about violations had been about. The quality of proof of the main violations alleged -- the Krasnoyarsk radar, a second new intercontinental missile and excessive encryption -- varies substantially. No claim is made that Soviet violations are militarily significant. Moscow alleges certain American violations. But the president is intent on conveying to the Soviets, who are his Geneva negotiating partner, that the United States means business about compliance.

There is one particular step, however, that Mr. Reagan is being urged to take under "proportionate response" that he should not take: to violate SALT II openly by drydocking (and leaving available for future use) the two Poseidons due to be replaced by the next new Trident in May, instead of dismantling them. Ragged as Soviet arms control compliance may have been, this would be the first officially sanctioned SALT II violation. It would assert a new American indifference and hostility to arms control. This is, of course, precisely, what the move's advocates feel is necessary to shake the United States free from what they see as an unfair and dangerous shackle on American security.

In fact, there are substantial reasons to hold to SALT II. Militarily, the Soviets are much better placed to exploit a "breakout": they have "hot" production lines, heavy missiles ready to take extra warheads, and no Gramm-Rudman. That's why, to the Joint Chiefs, "proportionate response" means going with current modernization plans. Politically, a breakout would put a heavy extra burden on the Geneva arms control talks whose promise is uncertain but essential to explore all the same.