A Soviet Embassy official declared yesterday that Andrei V. Berezhkov, the 16-year-old Soviet youth who is at the center of a diplomatic tug of war, "will leave the country," and several legal experts disagreed over the right of the State Department to stop his departure under the principles of international law.

A diplomat such as the boy's father, Valentin M. Berezhkov, and a diplomat's family is "inviolable" under international law, which means they are immune from being stopped, searched, detained or arrested, according to several experts in that area.

"I think it is questionable whether you can insist on the interview, if the sending state the Soviet Union does not want it," said Lee R. Marks, former deputy legal adviser at the State Department during the Carter administration.

The "real question" is whether you can demand custody of the boy in order to get the interview, Marks added. "It's a real tug of war with this boy in the middle."

Herbert J. Hansell, State Department legal adviser in the Carter administration, agreed that the case sets up a "tough legal tangle," but said he believes the "U.S. government would normally be entitled to to make the inquiries necessary to determine whether he Berezhkov has diplomatic status or not and whether he is eligible for asylum.

"To make those inquiries," Hansell said, "the government would normally be entitled to insist upon interviewing the boy."

A State Department spokesman said yesterday, "It remains our desire to ascertain the young man's intentions, and our position hasn't changed."

As to the legal grounds for that insistence, spokesman Alan Romberg said, "Our lawyers have reviewed the issue and advised us that the actions we are talking about are consistent with the law." Romberg refused to elaborate.

Meanwhile, the Soviet Embassy's number two official, Oleg M. Sokolov, visited the State Department again yesterday for a meeting, but Romberg refused to say what occurred at that session.

Sokolov, upon leaving the meeting, said, "We insist and continue to insist on an unhindered departure of Andrei Berezhkov and his family to the Soviet Union from the United States, without any prior interviewing by anybody from the U. S. authorities. This is our position of principle." He added that there had been "no progress whatsoever" toward resolving the matter.

A State Department official, who insisted on anonymity, said the youth is still believed to be in the Soviet compound on Tunlaw Road in Northwest Washington, and that no attempt has been made to move him.

The embassy's spokesman, Vladimir Mikoyan, said the boy is "with his mother and father." Still, the youth's whereabouts remained a mystery, as it has since last Thursday when letters, signed with his name, were received by the White House and The New York Times. The letter to the newspaper said, "I hate my country and it's sic rules and I love your country." The White House has not revealed the contents of its letter.

Legal experts outside the State Department said the question of legal grounds for demanding an interview with the boy brings several competing legal principles into play. None stated flatly that there could be no legal grounds, but all of them called the situation "muddy" or "complex."

Several pointed to the Refugee Act of 1980, which according to immigration attorney David Carliner, says that if someone has a "well-founded fear" of persecution in his home country, he has the right to seek asylum here and the U.S. has an obligation not to send him back that country. "Having written these letters, the boy does have a well-founded fear," Carliner said.

There is also a 1957 statute that says a diplomat or a member of his family may apply to the U.S. Attorney General for permanent residency, Carliner said. But the real conflict, Carliner and the others said, is how to get access to the boy.

Marks said that the youth himself cannot waive diplomatic immunity. A diplomat's country may waive it, for instance, to allow a diplomat to be questioned in court, as countries sometimes do. But the diplomat himself may not waive his immunity, according to Marks.

This is the biggest hurdle to the interview, the lawyers said.

The Berezhkov case is further clouded by the fact that the boy is, at 16, a minor. "Should a sovereign state accept the letter of a minor as a knowing and intelligent request for asylum?" one attorney asked.

Thomas Buergenthal, an international law expert and dean of the Washington College of Law at American University, said the question is even more difficult because the boy is 16. "If this was a child of 10, you could say, the parents should make the decision," Buergenthal said. "But then it gets harder as the child gets older.

"The question is, what age does he have to be to make those decisions," Buergenthal added. "It is not an easy question."