At least two White House guests at the summit-week state dinner will not be strangers to the visiting Soviets -- Van Cliburn and Mstislav Rostropovich. Piano virtuoso Cliburn, who in 1958 became the first American to win the Tchaikovsky Competition in Moscow, has been keeping a low profile professionally for nearly a decade. Now he has decided to play before an audience again, and what an audience! And this time there'll be no competition; his solo performance will follow the Dec. 8 dinner given that evening by President and Mrs. Reagan for Soviet leader Mikhail Gorbachev and his wife Raisa.

Unless there's a last minute change of plans, conductor-cellist Rostropovich -- who fled the Soviet Union in the 1970s -- will be dining, but not performing. Cliburn has been preparing a program including works by Chopin, Rachmaninoff and Brahms, but a full-time return to the stage is uncertain. "Let's wait and see how it goes," he said. "All I can tell you now is that I'm ready and will do my best."

Dressing Down Joan Rivers in GQ

Comedian and sometimetalk show host Joan Rivers' trademark, the rhetorical question 'Can we talk?,' is something she has never had trouble answering. Or so suggests her longtime friend Bert Hacker in a scathing story he has written for the December issue of GQ magazine. According to Hacker, Rivers' marriage to the late Edgar Rosenberg wasn't always blissful -- especially toward its end. Hacker says Rivers complained bitterly to him about her husband before his suicide in a Philadelphia hotel, during his funeral and afterward. Just before Rosenberg's death, Hacker says Rivers confided to him: "Things are just about finished with Edgar ... he's making me ... insane." Hacker says that when he reminded her that she and Rosenberg had been together a long time, Rivers replied, "So were Roy Rogers and Trigger." Following the funeral, Hacker writes, he overheard Rivers talking on the phone to a publicist who was setting up an interview with People magazine: "They owe me this one. Who's got a bigger story this week?!"

Smits' Courtroom Drama

"L.A. Law" attorney andresident hunk Jimmy Smits has just finished a real-life courtroom scene. Smits, 32, has pleaded no contest to a charge of disturbing the peace, in return for which charges of battery against a police officer and resisting arrest were dropped. His friend Wanda De Jesus, 29, faced the same charges and made the same plea. The charges stemmed from an Aug. 10 incident involving police at Smits' Los Angeles condominium. The two paid a total of $400 in fines and were ordered to perform a combined 125 hours of community service.

No Welcome Mat for Polanski

It looks as if filmdirector Roman Polanski won't be welcome in this country any time soon. Polanski, 54, whose films include "Rosemary's Baby," "Chinatown" and "Tess," was convicted of unlawful sexual intercourse with a 13-year-old model and aspiring actress nearly 10 years ago and fled to Europe while awaiting sentencing. There has been speculation recently in the press that the Los Angeles district attorney was reevaluating the case, but a spokesman in the prosecutors' office said, "By law, there's nothing the district attorney can do. If he {Polanski} returns, he'll have to face sentencing."

Schwarzenegger's Swing at Stallone

Arnold Schwarzeneggerflexes his mental muscles for Playboy readers in an interview in the magazine's January issue. The actor reveals, among other things, that he hates fellow actor Sylvester Stallone's wardrobe. "It's a shame no one taught him to be cool," Schwarzenegger says. "He should have L.L. Bean shoes and corduroy pants with a plaid shirt ... rather than that fur coat when he directs." He adds that he's the one who wears the pants in his family, not wife Maria Shriver. "Neither my mother nor Maria is allowed to go out with me in pants," he says. "Maria would never wear pants, believe me." Chuck Conconi has the day off.