The Soviet soldier who took refuge in the U.S. Embassy in Kabul last Monday returned to Russia's hands yesterday, ending a potentially serious Sovet-American standoff inside Afghanistan.

The State Department announced that Pvt. Aleksandr Kruglov -- whose name and rank previously had been withheld -- decided to leave voluntarily in the course of an hour-long meeting with the Soviet ambassador and other officials at the U.S. Embassy early Sunday, Washington time.

In the meeting, presided over by acting U.S. ambassador Hawthorne Mills, Soviet Ambassador to Afghanistan Fikryat Tabeyev promised the soldier that "he would be able to leave the Soviet army immediately and return to his technical education with no charges or penalties against him for having come to the American Embassy," according to the State Department.

Kruglov left with Tabeye within an hour after the meeting and after permission for his departure had been given by high officials in Washington over an open teletype line. The State Department would not say who gave the permission, but officials said the White House was kept fully informed.

The soldier's departure, which came almost as suddenly as his arrival at the embassy six days before, brought to an end a thorny human and political problem which had added new controversy to already strained U.S.-Soviet relations.

Kruglov's continued residence in the U.S. Embassy was an embarrassment to the Russians. And since the Soviets and the Soviet-dominated Afghanistan government were not cooperating with efforts to arrange for Kruglov to leave for the West, the situation threatened a lengthy standoff at the embassy.

The entire embassy staff had remained there during most of the past week because concrete barricades were erected outside and Afghan security forces sought to search any American trying to leave. The barricades and the harassment were lifted yesterday within an hour of Kruglov's departure, officials here said.

The State Department said it was satisfied that Kruglov's decision was made freely, without intimidation or pressure being used, and that it was made after careful and repeated explanations by a Russian-speaking American official of the options available to the Soviet soldier. These options included remaining in the U.S. Embassy for as long as he wished while efforts were made to arrange for him to come to the United States or a third country, the State Department said.

At U.S. officials' request Kruglov wrote a statement, released in translation by the State Department, that said "my decision about voluntary departure from the U.S.A. Embassy was not made under any kind of pressure."

On some occasions in the past Soviet officials have promised defecting citizens that no dire consequences would await their return, according to State Department officials. But such arguments have rarely been decisive, the sources said, and in any event there is no clear model or precedent for the present case.

Washington officials conceded it will be difficult if not impossible for the United States to learn whether the assurances given Kruglov are kept or what happens to him once he returns to Russia. The officials emphasized that the crucial thing in their view is that the soldier's decision was made voluntarily in a meeting held under controlled circumstances.

The United States as a matter of policy has permitted Soviet offficials to interview Soviet citizens seeking asylum if the person involved agrees. The United States asks for the same rights when the tables are turned. In this case, officials said, Kruglov agreed to the interview without hesitation. t

The Soviet soldier was depicted by officials here as an intelligent, perhaps even crafty, young man who came slowly to a realization of the practical options facing him as the week wore on. When the Russian ambassador made his offer, which some officials here depicted as unexpected, Kuglov is reported to have accepted it quickly.

Asked if Krulov had provided intelligence on Soviet military activities in Afghanistan, a State Department official said conversations with him had been limited to determining his background and his wishes in the situation, and explaining the options open to him.

In an attempt to make his future no more difficult than it is already, the United States declined to make public any details of his background or job or what had led him to seek refuge.

For the first several days after Kruglov's arrival, the United States was handicapped by the absence of any fluent Russian speaker at the Kabul embassy, which has now been reduced to fewer than 20 Americans, including Marine guards. A Russian-speaking political officer, Robert Ober, arrived from Moscow Friday with Soviet and Afghan government permission.

Washington officials said they could only speculate why the Soviets promised not to penalize Kruglov in their effort to convince him to return. One official suggested the Russians may have decided that more important aspects of the U.S.-Soviet relations should not be hindered by the case.