At last night's diplomatic reception honoring Martin Luther King Jr., D.C. Mayor Marion Barry and Soviet Ambassador Anatoliy F. Dobrynin, the hosts, stood ready to greet their guests in the great hall of the Organization of American States.

The line hadn't yet begun moving. Barry asked Dobrynin, who has served during six U.S. administrations, about his job situation since a new Soviet foreign minister, Eduard Shevardnadze, took over in July.

"For the time being I'm here, but nobody knows," Dobrynin said smilingly.

Beside the two men stood PepsiCo Inc. Chairman and CEO Donald M. Kendall, whose company paid for the food.

"You should be drinking a Pepsi," said a woman to Kendall, who was drinking something else.

The line moved and the three men -- the black American mayor, the stellar Soviet diplomat and the tycoon -- began shaking hands with the several hundred diplomats, their wives and other dignitaries who had been waiting.

There was a flurry when Coretta Scott King arrived and joined the three men at the head of the receiving line. She had met with President Reagan in the White House, and she seemed to be tired but her eyes had the misty, luminous quality that you can catch even in newspaper photographs.

Later when she got a chance to sit down, she said, "It was a cordial meeting, even I would say a friendly meeting. The president wanted to talk about the meaning of this day . . . He started out about my feelings and the sadness I might feel. He said, 'I'm sure you have mixed emotions,' and I said, 'Yes, but I also have my feelings of fulfillment as well.' "

Evangelist Billy Graham had already gone through the line when Coretta King arrived. He returned to greet her with a hug, and then the five of them -- Graham, King, Barry, Dobrynin and Kendall -- smiled and stood with their arms around one another for the photographers.

Graham said he and Martin Luther King Jr. had first worked together in 1954. "He told me, 'You keep them integrated in the stadiums and I'm going to go to the streets.' "

Graham also called Dobrynin a "warm friend," adding, "I'm glad to see what's happening now -- the new spirit developing between our two countries."

Nearby, Rep. Ralph Regula (R-Ohio) watched Dobrynin. Regula, a member of the federal commission implementing the holiday honoring Martin Luther King Jr., had approached Dobrynin earlier in the evening on behalf of a constituent in Ohio. The constituent's father, Regula said, lives in the Soviet Union and isn't being allowed to visit his son in the States.

"He said he'd look into it if I send a letter," said Regula. ". . . Sometimes you never understand their reasoning over there."

Martin Luther King Jr.'s 22-year-old daughter, Bernice, arrived with her mother. She said she was a small child when her father was assassinated.

"I'm happy, I'm proud," she said of the new national holiday honoring the slain civil rights leader.

"The Star-Spangled Banner" was played at the beginning of the formal remarks. The mayor and his wife, Coretta King and Kendall all had their hands over their hearts and sang the words as they stood on the stage. Dobrynin, unsmiling, stood beside them silently and kept his hands at his sides.

Barry spoke first, calling for an end to war and saying, "We must all learn to live together as brothers." He called King "a great American patriot and a hero to millions of people across the face and breadth of the earth."

As he spoke, many guests continued talking in the back of the hall and there was the clatter of dishes as people continued eating.

Then Coretta Scott King spoke, saying, "The Soviet ambassador has joined hands with us." She added, "There is so much yet to be done."

During her speech, too, the background noise of people talking and eating continued. She received polite applause.

Dobrynin read his speech quickly and in a heavily accented voice so that little of it could be clearly understood. He could be heard referring to "the ideal of peace" and the "danger of nuclear catastrophe."

The background noise grew even more intense during his speech, but he received approximately the same amount of polite applause as Coretta King.

Then Kendall spoke, saying he would be brief because Martin Luther King Jr. himself "did not like long programs unless he was the program." This didn't draw many laughs, and Kendall quickly sat down again after thanking everyone for coming.

Finally the Morehouse College Glee Club -- of which Martin Luther King Jr. was once a member -- got on stage, and as they began singing "We Shall Overcome" in low tones the background noise of voices and plates was still audible.

Many people who were trying to listen became irritated at the disruption.

"SHHHHHHHH!" said Mayor Barry, who was eating a crepe and trying to listen to the song.

But then their voices swelled and they sang it out good and loud, a hundred strong young male voices: "OHOH . . . DEEP IN MY HEART . . . I DO BELIEVE . . . WE SHALL OVERCOME . . . SOME DAAAAY . . . "

And they did, too.