Svetlana Stalin's plight may be news to some State Department Soviet experts, but not to her friends. Several in Washington have received letters from the 61-year-old daughter of the late Josef Stalin telling them that she is broke. "It is hard for me to beg," writes Stalin, who now goes by the name Lana Peters, from Spring Green, Wis. "But I must continue to write. This is my worst time I have ever met."

Peters wrote two books about her life and times in the late 1960s but says publishers are not interested in anything she has written since.

"The attitude towards me, after my return from USSR in 1986 (we stayed there for 18 months, I hoped to join my family there) is hostile," she writes.

She tells of living on borrowed money ("My own had been spent by my former husband and his son; the marriage was for my money only"), of which only $1,500 remains. She expresses the fear that she will lose her mortgaged Wisconsin home; friends describe it as modest and her car as old.

Her daughter Olga goes to a Quaker school in England and friends say they correspond regularly. The child's father is architect Wesley Peters.

On the farm front: Soviet agriculture chief Viktor Nikonov, a member of the Politburo and secretary of the Communist Party Central Committee, meets President Reagan tomorrow. Nikonov and his entourage -- the highest ranking Soviet delegation to come to the United States since Leonid Brezhnev and his crew in 1973 -- are here at the invitation of Rep. Kika de la Garza (D-Tex.), chairman of the House Agriculture Committee.

Nikonov, one of the Communist Party's Big Six, may or may not be the stalking horse for Mikhail Gorbachev's forthcoming summit visit, but certainly he'll go home to Moscow with plenty of ideas for what Gorbachev could see. In Washington, for example, he'll see a musical comedy (in this case, "Sweet Charity" at the National Theatre) tomorrow night after a Soviet Embassy reception in his honor. Thursday morning he goes to Falls Church to visit the Giant Food supermarket. Also on his itinerary are farms, research plants, a seed company and a commodity market in such cities as Chicago, St. Louis, Des Moines and Baltimore.

He'll also go to Disney World, where Mickey Mouse, dressed in overalls, is slated to greet him.

That was no pretender you saw in the lobby of the Grand Hotel Sunday night. That really was the king of Spain.

Juan Carlos and his 70-member entourage were en route to Madrid after a 10-day U.S. tour (Queen Sophia had gone home the day before on a commercial flight) when crews found a mechanical problem in the royal aircraft during a refueling stop at Andrews Air Force Base.

Grounded for the night, Juan Carlos and Co. were rescued by the U.S. Office of Protocol, which turned up 71 rooms at the 263-room Grand in 20 minutes flat.

At the hotel, the king, still unnerved from the earthquake that marked his Los Angeles trip, disappeared into the royal suite. But everybody else headed for the dining room, where the Grand's featured pianist, George Court, doubled as a waiter on his break; Khalil Yazbeck, one of the Grand's owners, carried trays; and General Manager Samir Darwich worked as a busboy.

What might have been one hotel man's nightmare turned into another's dream. Only that evening Darwich said he had told Court it was about time the Grand got ready for a kingly guest again (Jordan's Hussein was the last).

Denying he is clairvoyant, Darwich said, "I'm very glad we had a low {occupancy} weekend."

Japanese crown princes don't get into substantive matters. A "more fitting" topic, a Japanese Foreign Ministry spokesman said yesterday of Crown Prince Akihito's discussions on his first visit to Washington since 1960, "is long-term friendship."

Friendship it is, then, as Akihito and Crown Princess Michiko move around Washington, one of three U.S. cities remaining on an itinerary necessarily cut short because of 86-year-old Emperor Hirohito's recent surgery.

Akihito talks to his father every other day, the spokesman said, adding that the emperor's recovery from intestinal surgery is "very smooth and steady."

Yesterday the Japan-America Society gave a luncheon for the imperial pair. "To a great extent his life's work has been in preparation for the day when he will ascend the throne as the 125th emperor of Japan," said society President Marshall Green, a former assistant secretary of state for East Asian and Pacific affairs, in introducing Akihito.

Today, the crown prince meets with President Reagan, both in the Oval Office and again tonight over a private dinner for 40 at the White House. An accomplished cellist, Akihito has a treat in store. Entertaining him and Michiko, a talented pianist, will be cellist Yo-Yo Ma.

Tomorrow promises to be just as busy, with stops scheduled at a Walt Whitman High School Japanese language class, the Smithsonian to see the exhibit on the internment of Japanese Americans during World War II, and the U.S. Naval Observatory tennis courts, where Vice President Bush and Secretary of State George Shultz will be waiting, rackets in hand.

Also on the agenda tomorrow is a visit to the Washington Home and Hospice, where one of the 15 residents waiting to meet them will be Tokyo-born Eleanor Walker, 97. Walker met her husband on the same tennis court at Karuizawa, the Japanese summer resort, where Akihito and Michiko first met in 1959.

Tomorrow night, the crown prince and princess have invited the vice president and his wife Barbara Bush to dinner at the Japanese Embassy, where the star-studded guest list will include tennis champs Jack Kramer and Ann Kiyomura, Voyager copilots Dick Rutan and Jeana Yeager and movie star Brooke Shields. Shields' Japanese connection is the imperial couple's son Prince Hiro, whom Shields met last year on his way home from Oxford University.

"She was -- and is -- his favorite movie star," explained an embassy spokesman.

Elsewhere on Washington's diplomatic front, Mozambique's new president, Joaquim Alberto Chissano, met with President Reagan yesterday. He is the first of two African leaders scheduled for discussions here this week on southern Africa; Zambia's Kenneth Kaunda meets Reagan tomorrow.

Nancy Reagan goes to Chicago tomorrow to share the spotlight with Howard University's Dr. Roland Boyd Scott.

Scott, director of the Center for Sickle Cell Disease at Howard, will receive a $100,000 check from the Ronald McDonald Children's Charities for his work on sickle-cell anemia. A check for $100,000 also awaits Mrs. Reagan for her campaign against drug abuse. She's earmarked her check for the Nancy Reagan Drug Abuse Fund