Just when things on the Anglo-Soviet diplomatic front were proceeding rather nicely, the atmosphere between London and Moscow has suddenly soured. Both countries have been involved in an expulsions game in which the enforced departure of diplomatic personnel in one country has triggered retaliation in the other.
At this writing five Soviet officials had been ordered to leave London for ``activities incompatible with their status.'' That's simply code language for spying.
The determination of the British Government to take such action when both countries have been indulging in some mutual flattery is taken as a measure of the seriousness of these Soviet offences.
Still, government sources want to regard the spying incidents as something divorced from overall relations with Moscow, and hope that ties won't degenerate as a result. Their logic is that as much as warmer East-West relations are desirable they must not have precedence over risks to national security.
Although no official elaboration has been forthcoming, it is suspected that the Soviets might have been involved in trying to establish agents in Britain.
Only last May, Britain expelled Arkadi Gouk, a first secretary, said to be prominent in the KGB and the contact man in the trial of Michael Bettaney, the MI5 traitor.
Britain has also developed highly sophisticated antisubma-rine devices which have intrigued the Soviets. A possible link is suggested because one of the two Soviets expelled is the assistant naval attach'e.
Initially, the Foreign Office intended to publicize the expulsion of only two Soviet officials: Capt. Oleg Los, assistant naval attach'e at the Soviet Embassy, and Vyacheslav Grigorov, manager of charter operations with Aeroflot, the Soviet airline.
In a strategy which failed to enlist Soviet support the British government said three others would be allowed to leave the country quietly, provided the Soviet Union did not retaliate. The Soviets ignored the suggestion and promptly declared that Capt. John Marshall, British naval attach'e in Moscow, Lt. Comdr. Martin Littleboy, an assistant, and Carol Robson, a science attach'e, would have to leave Moscow.
The unexpected chill in Anglo-Soviet relations contrasts with the ebullience shown on both sides in recent months.
Despite Mrs. Thatcher's ``Iron Lady'' image (the term was coined by the Soviets), the prime minister was taken with the affability and warmth of Mikhail Gorbachev on his visit to Britain shortly before he was made Soviet leader. Thatcher declared publicly that she liked him and could do business with him.
The diplomatic guess here is that the Soviet Union takes a realistic view over the penalties that come with spying, and that Gorbachev will be reluctant to let the affair stand very long in the way of his desire for better East-West relations.