Nancy Reagan will attend a private memorial service in New York today for the late publisher Gardner Cowles, the White House announced yesterday. Cowles, who was the founder of Look magazine and part of the Cowles media empire, died of heart failure July 8 at age 82. Mrs. Reagan and the publisher were well acquainted, said Elaine Crispen, the first lady's press secretary . . .

Olga Hirshhorn, widow of Joseph H. Hirshhorn, whose collection of modern art forms the Smithsonian's Hirshhorn Museum and Sculpture Garden, was married Sunday to Robert Whittier Dudley, a Washington lawyer and businessman. The wedding was held at Dudley's vacation home in Sharon, Vt., and was attended by immediate family and close friends . . .

Actresses Jessica Lange and Sissy Spacek, who both recently starred in movies about American farmers, will be the masters of ceremonies at the Sept. 22 Farm Aid benefit concert, organizers said yesterday. The concert, which will feature nearly 40 rock, country and blues entertainers, will raise money to help the nation's farmers. Lange, who starred in "Country," and Spacek who starred in "The River," both confirmed they would appear and host the Champaign, Ill., concert, said Ellen Golden of the Howard Bloom Agency in New York, which is handling publicity for the event . . .

Former president Richard M. Nixon arrived in Peking Tuesday for a six-day visit to "see my old friends." He made his first visit there in 1972, as the first U.S. head of state to go to China; this trip is his fifth . . .

A car once owned by Adolf Hitler, a 1934 Mercedes 770K limousine, went unsold Monday at a classic car auction in Auburn, Ind., because the $200,000 top bid did not meet the owner's asking price. The car was captured by the Free French Army at Hitler's mountain retreat at Berchtesgaden. After displays in Paris, Montreal, Toronto, Detroit and Syracuse, N.Y., the vehicle was purchased by a private investor and has been in storage for years . . .

Lynette (Squeaky) Fromme, who is serving a life sentence for attempting to assassinate former president Gerald Ford in 1975, has declined an opportunity to seek parole, officials said Tuesday. "She has not given us any reason for not having this hearing," said David Helman of the Federal Correctional Institution for Women in Alderson, W.Va. "I don't know what her thinking is, but it's not uncommon. Some inmates don't think they have much of a likelihood of gaining parole anyway . . ."

Stephen King, known for his horror novels, is making his directorial debut this summer in the movie adaptation of his story "Overdrive." Says King: "Directing is very interesting and very hard. The only difference between this and working on a road gang is that the pay is ever so much better."