Arkady N. Shevchenko, the highest-ranking Soviet official in the United Nations secretariat, has left his post claiming "differences with his government" and has informed the State Department that he does not intend to return to Moscow.

A State Department spokesman said last night that Shevchenko, 47, undersecretary-general for political and Security Council affairs, informed U. S. officials of his decision last week through his American lawyer, Ernest Gross.

U. S. officials said privately that Shevchenko so far had not made any request for political asylum and it was not clear whether he could be regarded as a defector. If he does request asylum, he would apparently be the highest-ranking Soviet citizen ever to defect to the United States.

U. N. sources said last night that the door to Shevchenko's office at the secretariat building in New York had been sealed. The sources added that his wife and a teenaged daughter had left New York for the Soviet on Sunday.

After the U. S. government informed the Soviet Union and the United Nations of Shevchenko's intentions, the Soviets requested a meeting with him, the department spokesman said.

Such a meeting has been arranged by Gross, the spokesman added. He did not say, however, when it would take place, and he gave no indication of Shevchenko's present whereabouts.

A department statement said the United States "in no way attempted to influence him in his decision." It added that, until Shevchenko is fired or quits his U. N. position, he is considered to be legally in this country and entitled to the protection of U. S. law.

The case came to light earlier yesterday when the United Nations released a guarded statement saying Shevchenko had left his post because of "difference with his government" and that he was being placed on leave while efforts were made to clarify the matter.

As one of 32 undersecretaries-general, Shevchenko was the senior of the 191 Soviet citizens among the 18,500 people from 125 countries employed by the secretariat. His position gave him a rank immediately below Secretary General Kurt Waldheim, and he received a gross annual salary of $76,000.

The major secretariat posts are apportioned among U. N. member countries on a quota basis. Since they are filled on the recommendation of the governments controlling the positions, Shevchenko was the official chosen by Moscow for his position.

Before assuming the U. N. post in April, 1973, Shevchenko, a native of the Ukraine, had been a career diplomat in the Soviet foreign service. In the 1960s, he served seven years in the Soviet U. N. mission and became a specialist in disarmament questions.

In 1970, he became a disarmament adviser to Soviet Foreign Minister Andrei Gromyko and was given the rank of ambassador. Diplomatic sources said his interest in disarmament continued after he joined the secretariat, and he had been in charge of planning a special U. N. session on disarmament scheduled for May.

Western diplomats privately described him as a doctrinaire Communist who openly used his post to advance Soviet interests. In 1976, Shevchenko was the central figure in a controversy that saw the British and Japanese delegations charge him with trying to pressure them into supporting an increase in his division staff.