Yesterday's announcement that Soviet Ambassador Anatoliy Dobrynin will return to Moscow means that Swedish Ambassador Wilhelm Wachtmeister will become dean of Washington's 153-nation diplomatic corps.

As No. 2 in seniority in the diplomatic corps, Wachtmeister automatically will succeed Dobrynin as dean. But ever the perfect diplomat, he declined to comment on his ascension yesterday because protocol dictates that he be notified officially by Dobrynin, who is in Moscow for the 27th congress of the Soviet Communist Party.

"We presume he will come back to make final calls and to depart from this country," said Soviet Embassy spokesman Boris Malakhov.

For Dobrynin, Moscow's man in Washington for 24 years, the right diplomatic moves often have been over a chessboard. For Wachtmeister, who has been here 12 years, they've been on the tennis courts.

Both are men who know that getting things accomplished in Washington's high-stakes game of international diplomacy takes more than strong-arming across the conference table.

During the Carter administration, for instance, both played national security affairs adviser Zbigniew Brzezinski, Dobrynin at chess and Wachtmeister at tennis. And both played to win.

"What I notice about these people is they're all very competitive," said WDVM-TV sportscaster Glenn Brenner, who has been in tennis tournaments with Wachtmeister. "They play for keeps. They take no prisoners."

Dobrynin, who is being called back to the Soviet Union to be the secretary of the Communist Party's Central Committee, is credited with changing the stuffy, forbidding image of Soviet envoys.

"Any Soviet ambassador would carry a lot of weight, but he was always such a friendly man, always radiating a friendly atmosphere," Austrian Ambassador Thomas Klestil said yesterday. "In times of tensions, he seemed eager to talk. He was the living example of coexistence."

Wachtmeister is described in similar terms.

Charles Z. Wick, director of the U.S. Information Agency, yesterday described the Wachtmeisters as "unfailingly charismatic, genteel, terribly popular people. His style of doing things has earned him all that affection."

Swedish newspapers speculated last month that Wachtmeister was going to be called back to Sweden and replaced by another ambassador, but an embassy spokesman said yesterday that "no decision" has been made on such a move.

Some diplomatic observers here think that if such a move were being considered in Stockholm, the prospect of Wachtmeister becoming dean would likely discourage it.

Although unofficial, the dean's position is, nevertheless, a plum that brings high visibility to its occupant and his country. The dean is pivotal in the diplomatic corps' relations to the host country; he represents its members when questions of privilege or immunity arise.

"When there are matters of policy -- any kind of problem that affects the corps -- I discuss them with the dean," said Chief of Protocol Selwa Roosevelt.

A major part of the dean's job is ceremonial. He is the first in line at a diplomatic reception or dinner given for chiefs of missions by the president or secretary of state. He sits on the right of the president's wife or the wife of the secretary of state. He also is expected to give the responding toast on behalf of the corps.

As vice dean, Wachtmeister will be the one responding tonight when Secretary of State George Shultz entertains the chiefs of diplomatic missions, because Dobrynin is in Moscow.

Born to the Swedish nobility, Wachtmeister, 63, entered the foreign ministry in 1946. His early career was distinguished by his appointment as personal secretary to then-United Nations Secretary General Dag Hammarskjold in 1958.

He has served in diplomatic posts in Moscow, Vienna, Madrid and Lisbon, and was Sweden's ambassador to Algeria. Before coming to Washington in 1974, he was head of the political office of Sweden's foreign ministry for eight years.

Almost from the moment he and his wife Ulla arrived in Washington, they were instant stars in the Embassy Row social set. Countess Wachtmeister quickly made a name as a gracious hostess; an invitation to the Swedish Embassy is among the most sought-after in town.

"It's a matter of personal style. She can take a little bit of nothing and turn it into something special," said a friend. "She has a chef but no staff of servants. She's a wonderful cook as well as hostess."

Countess Wachtmeister is also an accomplished artist. But she leaves tennis to her husband. Their embassy courts on Nebraska Avenue NW are a popular gathering place for some of Washington's most powerful officials. Among Wachtmeister's frequent partners is Vice President George Bush.

"It's important the way you get your exercise in Washington," said Wick. "My impression is that tennis in Washington is not like some people use golf -- a social tool. Anybody who plays tennis here finds somebody and finds a court, and then it's almost like being part of the mystical clan."

Today, Wachtmeister will preside at a memorial service in the National Presbyterian Church for Olof Palme, Sweden's prime minister who was assassinated last week in Stockholm.

If Wachtmeister becomes dean, vice dean will be Iceland's Ambassador Hans G. Andersen, 67, who came to Washington in July 1976. His wife Astridur also is an artist.