"I can confess to you, Mr. President, that after tonight's dinner, international communications will be overcrowded with messages sent abroad from Washington embassies," Soviet Ambassador Anatoliy Dobrynin told a chuckling audience of 160 diplomats and their spouses at the White House last night. The thought may have rung true, for many laughed knowingly.

"It is quite possible that practically each diplomatic cable will start with the proud verse 'Tonight I had personal conversation with President . . . and he told me 'so and so.' "

In his toast at the second of two formal dinners for the diplomatic corps, Reagan told his guests, "Napoleon is quoted as having instructed one of his ambassadors in the art of diplomacy by saying 'Keep a good table and look after the ladies.' It is our honor to set a table for you, and indeed a pleasure to entertain so many charming and beautiful ladies."

The dinner was a tradition revitalized from the Eisenhower years. Dobrynin, the dean of the corps, was in Moscow last week and could not attend the first dinner. After his toast, the Soviet ambassador, his wife and the others lined up single file throughout the Blue Room for a word with the president or first lady.

For many, the fancy dinner of veal was their first White House experience. "This is a great beginning for me," said new Israeli Ambassador Moshe Arens. "The first time I was ever in the White House was Tuesday when I presented my papers, and now this. It's quite impressive."

His long-range goals for his U.S. tour? "That I might make my modest contribution for Mideast peace."

"This is the highlight of our three years here," said Uzra Husain, wife of the Bangladesh ambassador. "It's a real treat because it's the first time for many of us."

Many of the women seemed anxious to meet the first lady, and lined up without prompting. Others stood shyly to the side and waited for someone from the State Department to guide them. The wife of the Honduran ambassador used the opportunity to send a message to the president. "You must tell your husband," she said, "that we want peace in Central America."

Mrs. Reagan chatted with Pilar de Llado, wife of the Spanish ambassador, about daughter Patti Davis' plans to travel to Spain. "My daughter is going to Valencia in March--They'll be shooting a movie," she said. "She's never been there. I'm sure she'll love it."

And, with the combination of the White House and half the diplomatic corps, some protocol confusion may be unavoidable.

"Can we go home now or do we have to wait until Anatoliy leaves," whispered one ambassador's wife to another.

"Who knows," the other shrugged. And off they went into the crowd of black ties and silk to find their way home.