As surely as day follows night, or vice versa, the Soviets came back at President Reagan on charges of cheating on arms control. He tossed out his charges against them in a letter to Congress dated Jan. 23. It cited ''seven different matters of serious concern regarding Soviet compliance.'' They came back Jan. 29 with the allegation of a ''wide range'' of United States violations of the same agreements that supposedly regulate nuclear weapons.
One high official who took part in the arms control negotiations remarked that much of the trouble involved in this current round of mutual recrimination is the result of having been unable to agree on specific terms.
He cited as an example of ambiguity now plaguing US-Soviet relations the matter of ''encryption.'' The nuclear test ban treaty prohibits such coding of the ''telemetry'' of tests as would ''impede verification.'' It does not prohibit all ''encryption,'' only such as would ''impede verification.''
Well, the Soviets code much of the information coming from their tests. They claim that enough is left over for verification. Washington says it isn't enough. There is no higher court to decide what quantity of ''encryption'' does or does not ''impede verification.'' My source says that those involved knew at the time of treaty drafting that this ambiguity would cause trouble in the future. It has.
Five of the seven items on the US list of charges against the Soviets involve the SALT I and II agreements. Four of the five are in the category of ''possible ,'' ''probable,'' or ''almost certainly.'' Only one is said to ''constitute a violation.'' That one is the matter of ''encryption.''
Another item on the US list is the matter of the Soviets testing an antiballistic missile in a forbidden manner. The agreements prohibit firing an antiballistic missile in company with a ballistic missile. It is ''OK'' to fire an antiballistic missile for testing, but not in such a way as actually to intercept a ballistic missile in the air.
My informant said that the Soviets did this twice. ''We detected it each time and called them on it. They apologized and said it was a mistake. We of course thought they did it deliberately to test our verification ability.''
The main countercomplaint from Moscow is over wooden sheds that were built over the silos containing US Minuteman II missiles. The silos were going through a process of rebuilding to improve their blast resistance. Also, some of their contents were converted from Minuteman IIs, which carry a single warhead, to Minuteman IIIs, which carry three warheads.
The Soviets complained that when the sheds were removed they had no way of verifying which contained the single- and which the triple-warhead weapons. The American answer was to mark the lids. But the Soviets said they had no way of knowing whether the markings were true or false.
The problem of verification comes out in both sets of complaints. Another example involves the limit of 150 kilotons for underground tests. The President's letter says the Soviets have probably gone higher. But my informant tells me that measurement of a blast could be accurate only if the rock formation at the site of the blast were known.
Obviously, both sides have padded their lists of complaints with everything they could think of to make it more impressive. The complaints have all been registered before through diplomatic channels. The matter of the American sheds over the Minuteman silos and the Soviets setting off ABM shots to intercept ballistic-missile shots dates from before Mr. Reagan took office.
What is new is that the President chose to go public with the American list of complaints and the Soviets, inevitably, whipped out their counterlists. The issue of alleged violations was a diplomatic matter. Now it is in the area of the propaganda battle. The effect is to underline the difficulties of verification, and also the difficulties of drafting rules and regulations so precise that there is no room for ambiguity.