Sifting evidence of Soviet violations

Recent disclosures about probable Soviet treaty violations show pointedly that checking on compliance can be the most difficult arms control issue. And they show that ambiguous wording in a treaty can lead to mischief.

The Reagan administration's report to Congress on alleged Soviet violations takes a low-key but clear line. Without resorting to ''evil empire'' rhetoric, it lists the areas where United States officials believe Moscow has ''almost certainly'' or in some cases ''probably'' broken arms control treaties or agreements.

At a time when the administration is trying to improve US-Soviet relations, the administration is letting the evidence speak for itself. But in doing so, it has also shown how subjective the world of arms control can be - that facts are not necessarily agreed upon - and why the White House is so wary of seeking further agreements.

By raising these charges, the administration is also reopening questions and criticisms about possible US violations if certain military modernization programs sought by the Pentagon are completed.

The report to Congress comes in response to orders from 93 senators, so the concerns are bipartisan in nature. And arms-control advocates usually critical of the administration say they are worried about possible Soviet violations as well.

''Violations of arms control agreements by any nation cannot be overlooked or excused,'' declared three former senior US arms control officials in a statement on Wednesday.

Yet these men - Gerard Smith, chief SALT I negotiator and former director of the Arms Control and Disarmament Agency (ACDA), Paul Warnke, SALT II negotiator and former ACDA director, and Herbert Scoville, former CIA deputy director and Arms Control Association president - also criticized the administration for publicizing at this time charges that have been known for months and in some cases years.

''Presidential public accusations of bad faith before all consultative or diplomatic avenues have been exhausted only prejudice the eventual resolution of the issues and make more difficult, if not impossible, achievement of our basic security objective of reducing the risk of nuclear war,'' they told reporters.

They asserted that the violation questions should have been pressed further with the Soviets privately through the Standing Consultative Commission established to monitor the SALT I and II strategic arms agreements signed by the two countries.

Administration officials contend that Soviet representatives to the commission either ignore US charges or draw out discussions for long periods without answering the charges. Critics are reminded that the administration - far from politicizing the issue - is responding to a broad bipartisan congressional mandate to report on Soviet violations. And even arms control activists admit that some treaty provisions make questionable activity, if not outright violations, possible.

Mr. Warnke acknowledges that the treaty he negotiated - SALT II - was purposely fuzzy on the subject of encoding data transmitted from test missiles. ''We wanted a certain amount of wiggle room, and therefore we gave them a certain amount of wiggle room,'' he said.

Arms control advocates are concerned that certain administration statements and actions could undercut arms control gains already won. Deploying the MX and single-warhead ''midgetman'' missile runs counter to the SALT II treaty (which was not ratified by the US Senate, but which both superpowers say they respect) limiting each side to one new missile.

And pushing forward with antisatellite weapons and ballistic missile defenses (as envisioned in the President's so-called star wars speech of last spring) could signal Moscow that the US intends to disregard the Antiballistic Missile (ABM) Treaty, some experts warn.

The administration asserts that by proceeding cautiously with research and development on a missile defense system it is only being practical. If the Soviets are about to field their own new ABM system, it is said, then the US must be prepared to respond. Alleged Soviet treaty violations at a glance Strategic Arms limitation Treaty II of 1979

* Flight testing more than one new ballistin missile. SALT II limits the US and USSR to one new light missile each. The Soviets have designated the SS-X-24 as this new missile, but US officials say another new missile, the SS-X-25, has been tested as well.

* Deployment of the mobile SS-16 intercontinental ballistic missile, which is prohibited bu the treaty.

* Encoding missile test data. Under SALT II, the US and USSR must openly broadcast certain flight-test data so that the other side csan check on compliance. The Soviets are charged with encrypting too much of this data. Threshold Test Ban Treaty of 1974

* Conducting underground atomic explosions larger than those allowed buy the Threshhold Test Ban Treaty. The agreement allows tests up to 150 kilotons, but US officials say the Soviets have tested devices with yields of up to 300 kilotons. Antiballistic Missile Treaty of 1972 (Part of SALT I)

*Building a large radar system in the Soviet interior to defend against ballistic missile warheads. The ABM Treaty limits US and Soviet missile defense sysems. Geneva Accords of 1925 and 1972

*Using chemical and toxin weapons in Afghnistan and Southeast Asia. Such weapons as ''yellow rain'' are prohibited by the Geneva agreement. Helsinka Conference on European Cooperation and Security of 1975

* Holding a large East bloc military exercise in 1981 without notifying the West. In 1975, 35 nations -- including the USSR -- agreed to publicize such maneuvers in advance.