That certainly was former Democratic presidential candidate Walter Mondale lunching at Mel Krupin's yesterday with former Democratic chairman Robert Strauss. And at the next table was another former Democratic Party presidential candidate, George McGovern, who dropped by for a chat. They were probably discussing such geological phenomena as avalanches or tidal waves and their good feelings about the District of Columbia and the states of Massachusetts and Minnesota . . . And at a party thrown by current Democratic National Committee Chairman Charles T. Manatt to show off the new DNC headquarters on Ivy Street, who should stop by but Frank Fahrenkopf. Manatt threw his arms about his Republican counterpart and showed him around the new digs. When Fahrenkopf was asked what he was doing there, he first said, "I don't know." Later he decided to answer, "Spying, what else?" . . . Pulitzer Prize-winning author John Hersey remained in George Washington Hospital yesterday, listed in fair condition. He collapsed Tuesday night during a reading at the Library of Congress . . . "George Stevens: A Filmmaker's Journey" and its director, George Stevens Jr., won the Gold Plaque Special Jury Prize at the Chicago Film Festival last week. The film, about Stevens' father, was the unanimous selection of a jury headed by noted Greek film director Michael Cacoyannis . . . Television star Steve Allen, who is performing at Charlie's Georgetown this week, is also taping segments of his PBS show, "Inside Your Schools." Today he will have sessions at Madison High School and Louise Archer Elementary School, both in Fairfax County. Last night Robin Weir, who often does Nancy Reagan's hair, stopped by Charlie's at Allen's request that he do the entertainer's hair . . . WMAL personality Johnny Holliday was in Cleveland last week visiting old friends from his radio days there when he decided to stop by the nursing home where the 92-year-old Cleveland television personality Dorothy Fuldheim is recovering from a stroke she suffered last summer. "Just as I was leaving her room with all the plaques and mementoes on the wall, she looked up and thanked me for coming, adding, 'Nobody remembers you when you're not on top anymore.' " . . .