Poor Uruguay. More than 30 years since its last state visit and then, when its president finally gets here, official Washington is distracted by the surprise announcement that the chief justice will soon step down.

The official pleasantries went on as usual at last night's state dinner, with President Reagan greeting President Julio Sanguinetti on the north portico. Even then, though, reporters took the opportunity to ask Reagan if he had been "shocked" when Justice Warren Burger told him in May that he would be leaving.

"It was a surprise, yes," Reagan said.

Earlier in the day at Secretary of State George Shultz's luncheon for him, Sanguinetti did not know why State Department spokesman Bernard Kalb was wandering from table to table whispering in people's ears. On Sanguinetti's right was Millicent Fenwick, U.S. representative to the United Nations Agencies for Food and Agriculture, who didn't know, either: She said at the dinner that she had only heard about Burger on the radio shortly before arriving at the White House.

"I don't think there'll be any great change," Fenwick told reporters.

"This is my unofficial -- I shouldn't be talking like this. I saw Justice O'Connor at the lunch. I was of course longing to have a little chat with her. I've been meaning to write her a letter -- I haven't always agreed with everything she's done but I didn't think it quite proper for people to lean on the Supreme Court."

O'Connor herself was clearly surprised at the Shultz luncheon when Kalb informed her of Burger's announcement and also that Associate Justice William Rehnquist would succeed him.

* "Yes, totally," she said when asked. "Well, yes, I was."

*She was also "thrilled," she said, about the nomination of Rehnquist and of U.S. Court of Appeals Judge Antonin Scalia to succeed him.

" 'Fabulous!' -- that's the word she used" when she heard Rehnquist's name, Kalb said.

And of Scalia's name: "She knew it immediately," Kalb said. "I said, 'Madame, I don't have it exact' and she gave me his first name."

Attorney John O'Connor, the associate justice's husband, explained the instant name recognition after the lunch broke up and people were crowding around to hear what his wife might be saying.

"We know him very well," John O'Connor said. "Socially. And he and Sandra were on the Anglo-American Legal Exchange together. We're friends."

The O'Connors are also friends -- longtime friends -- of Rehnquist's. "I've known him since I was 17 years old at Stanford University ," John O'Connor said. "Sandra and he were in the same law school class 1952 at Stanford."

Asked how she thought the Rehnquist and Scalia nominations will affect the balance on the Supreme Court, Justice O'Connor said, "I think they're two wonderful selections, couldn't be better."

Her husband's answer to the same question: "Well, Scalia is certainly regarded as a conservative."

At last night's dinner, the exchange of toasts by Reagan and his guest focused on historical ties between the United States and Uruguay and completely avoided any current issues, domestic, international or bilateral.

Sanguinetti's toast, given in Spanish and translated, was notable for its length and historical detail. He spoke mainly about 19th-century Uruguayan history and explained to a guest during after-dinner coffee that his wife is a professional historian.

Actor Stacy Keach was seated between Nancy Reagan and Princess Elizabeth of Yugoslavia, the mother of actress Catherine Oxenberg.

"We discussed all kinds of things," said Keach, who spent time in a British jail on drug charges and is now active in anti-drug abuse campaigns. "Everything from raising children to raising animals. We discussed big dogs, little dogs, soccer, American history and drug abuse, which is a favorite topic of the first lady."

Soccer was a topical subject due to Uruguay's loss in the World Cup competition to Argentina on Monday; raising children, because Keach will be married this Sunday to Malgosia Tomassi. What he learned about soccer must remain forever unknown, but Keach did reveal that Princess Elizabeth advised him to consider having triplets "and get it all over with."

Other guests included Sarah Caldwell, artistic director of the Opera Company of Boston, developer Oliver T. Carr, Reagan's surgeon Steven Rosenberg, chief of surgery at the National Cancer Institute, actor Tim Reid, actress Karen Valentine, NBC News President Lawrence Grossman and Rep. Claude Pepper (D-Fla.).

Guests dined on crab, lobster and cucumber mousse with "bow tie" cheese twists; medallions and quenelles of veal vol-au-vent, and an exotic mousse with praline sauce.

As usual, what women were wearing was part of the evening's color. Nancy Reagan drew all eyes with her gown, a beaded bodice in white, yellow and black with deeply slit white skirt. Catherine D'Alessio, president of Chanel Inc., assured everyone she was indeed wearing Chanel. "Always Chanel. All my life. My first grown-up suit from my mother was a Chanel suit fitted by Mademoiselle."

Princess Elizabeth, in Washington researching a book on the prewar history of her homeland, wore an extremely low-cut Giorgio Sant'Angelo.

And Lili Zanuck, wife of producer Richard Zanuck, was surrounded by monumental white ruffles. "I think I'm the ultimate fashion victim, don't you think? It's British. Is that treason?"

The evening's icing was the jazz artistry of the Dave Brubeck Quartet, which included Brubeck's son Chris. After an encore of "Take the A Train" that had even the crystal chandeliers twirling, President Reagan told Brubeck, making his sixth White House appearance: "I don't know how much easier you could shed 50 years in so short a time."

*Maureen Reagan told Uruguayan Sen. Jorge Batlle, who specialized in American jazz during a radio career before entering politics, that Brubeck had been brought in just for his benefit. Batlle said he didn't believe it for a minute, but it was a nice thought -- especially since the last time there was a Uruguayan president in the White House on a state visit, it was his father Luis Batlle.

The guest list for last night's White House dinner for the president of Uruguay:

Uruguayan President Julio Mari'a Sanguinetti and Marta Canessa de Sanguinetti

Armando Tommasino, president of the Supreme Court

Enrique Iglesias, minister of foreign affairs

Ricardo Zerbino, minister of economy and finance

Jorge Sanguinetti, minister of transportation and public works

Hector Luisi, ambassador of Uruguay, and Blanca G. de Luisi

Jorge Batlle, member of the Uruguayan Senate

Pedro W. Cersosimo, member of the Uruguayan Senate

Luis Ituno, president of the Chamber of Deputies

Prof. Humberto Ciganda, president of the Council of the Civic Union Party

Ricardo Pascale, president of the Central Bank of Uruguay

Gen. Guillermo de Nava, chief of the military household

Elliot Abrams, assistant secretary of state for Inter-American affairs, and Rachel Abrams

J. Patrick Barrett, chairman, Avis Inc., and Christine Barrett

Sen. Lloyd M. Bentsen (D-Tex.) and B.A. Bentsen

James H. Billington, director, Wilson Center, and Marjorie Billington

Richard Nelson Bolles, author, "What Color Is Your Parachute?," and project director, National Career Development Project, and Carol Bolles

Bradford R. Boss, CEO, A.T. Cross Co., and Alice Boss

Edward A. Brennan, chairman, Sears, Roebuck and Co., and Lois Brennan

Dave Brubeck, jazz pianist, and Iola Brubeck

Vice President George Bush and Barbara Bush

Sarah Caldwell, artistic director and conductor, The Opera Company of Boston

Oliver T. Carr, Oliver T. Carr Co./Developer, Willard Hotel

William J. Corbett, vice president, American Institute of Certified Public Accountants, and Ann Corbett

Catherine D'Alessio, president, Chanel Inc.

Jack L. Davies, Schramsberg Vineyards and Cellars, and Jamie Davies

Princess Elizabeth of Yugoslavia

Robert F. Erburu, president, Times Mirror Co., and Lois Erburu

Millicent Fenwick, U.S. representative to the United Nations Agencies for Food and Agriculture, Rome

JoAnn Isaacson Fray

Gen. Charles A. Gabriel, chief of staff of the Air Force

Marcella Ganoza

Michael R. Gardner, chairman, U.S. Telecommunications Training Institute, and Theresa Gardner

Rep. William F. Goodling (R-Pa.), and Hilda Goodling

Maurice R. Greenberg, president, American International Group Inc., and Corinne Greenberg

Lewis P. Grinnan Jr.

Lawrence K. Grossman, president, NBC News, and Alberta Grossman

Albert Hadley, interior designer

James Hoge, executive editor, New York Daily News, and Sharon Hoge

Sen. Robert W. Kasten Jr. (R-Wis.) and Eva Kasten

Stacy Keach, actor, and Malgosia Tomassi

Robert D. Kroger and Johanna Kroger

Sidney Kent Legare

Gerald Levy, chairman, U.S. League of Savings Institutions, and Ellin Levy

Rep. Dan Lungren (R-Cal.), and Bobbi Lungren

Donald MacGillivray and Mary MacGillivray

William J. McDonough, executive vice president, First National Bank of Chicago, and Suzanne McDonough

Rep. Claude Pepper (D-Fla.) and Frances Campbell

Adm. John M. Poindexter, assistant to the president for national security affairs, and the Rev. Linda A. Poindexter

Maureen E. Reagan

Donald T. Regan, chief of staff to the president, and Ann Regan

Tim Reid, actor, "Simon and Simon," and Daphne Reid

Selwa Roosevelt, chief of protocol, and Archibald B. Roosevelt Jr.

Dr. Steven A. Rosenberg, chief of surgery, National Cancer Institute, and Alice Rosenberg

Russell A. Rourke, former secretary of the Air Force, and Judith Rourke

Barrett Seaman, White House correspondent, Time magazine, and Laura Seaman

Arthur A. Seeligson Jr. and Linda Seeligson

Ruth Collins Sharp

George P. Shultz, secretary of state, and Obie Shultz

Robert A.M. Stern, architect

Vance Stickell, executive vice president, Los Angeles Times, and Betty Stickell

Antonio Valencia, president, Mexican and American Foundation, and Gloria Valencia

Karen Valentine, actress, and Gary Verna

Sen. Malcolm Wallop (R-Wyo.), and French Wallop

Margaret Warner, White House correspondent, Newsweek magazine

Caspar Weinberger, secretary of defense

Malcolm R. Wilkey, U.S. ambassador to Uruguay, and Emma Wilkey

Walter Williams, economist, George Mason University, and Conchetta Williams

Richard B. Wirthlin, pollster, and Geralie Wirthlin

R. Frederick Woolworth and Priscilla Woolworth, Coe-Kerr Art Gallery

Richard D. Zanuck, producer, and Lili Zanuck