London — Britain has decided to adopt stringent measures to rid the country of Soviet agents burrowing for Western defense secrets. The first senior victim of the Thatcher government's new antiespionage drive was the KGB's controller in London. Arkady Gouk, who had the rank of first secretary at the Soviet Embassy, was ordered to leave Britain May 22 after being named as a KGB agent during the recent trial of a British MI5 agent-turned-spy.
The Soviets immediately struck back, expelling the chief security officer at the British Embassy in Moscow. He had given evidence earlier in the month at a London inquest into the death of a British banker who fell to his death from his flat in the Soviet capital.
Sources in Whitehall say Prime Minster Margaret Thatcher is fed up with blatant Soviet spying in Britain and is determined to put an end to it. The British mood is being compared to that of 13 years ago when, at a single strike, the then Conservative government ordered 105 Soviet diplomats out of the country.
The expulsion of Mr. Gouk, coinciding with private warnings to the Russians that similar treatment may be meted out to other KGB operatives, comes at a delicate moment in British-Soviet relations. The foreign secretary, Sir Geoffrey Howe, following his trip to China earlier this year, is due to visit Moscow in July.
There are British fears that if Mrs. Thatcher appears too belligerent toward Soviet espionage activities, the Russians may tell Sir Geoffrey that he is not welcome in Moscow.
This would be a major setback for Mrs. Thatcher who, despite her reputation as the ''Iron Lady,'' has set course on a policy of closer contacts with communist governments.
But the prime minister is being pressed by the United States to clamp down on espionage that is likely to damage Western security interests.
A special target of the Russians has been the government communications center at Cheltenham, where one security officer was proved to have leaked important intelligence secrets to the Soviets.
Whitehall officials say Britain's open society, coupled with the apparent casualness of many civil servants, encourages the Soviets to think there are easy pickings here for a spy.
George Walden, an outspoken Conservative member of Parliament, was a foreign office diplomat at the time of the 1971 expulsions.
''A middle-ranking country like Britain can too easily find itself being bullied by the Russians into accepting espionage as an unavoidable fact of life, '' Mr. Walden says.
''We must take tough action to prevent this happening.''