Last night at a benefit for the RFK Journalism Awards, "Citizen Kane" was billed as the draw, but the nearly 200 guests seemed just as interested in "Citizen Mankiewicz."

Frank Mankiewicz, who serves as a member of the RFK Awards Committee, which recognizes outstanding coverage of the disadvantaged and their problems, is the son of Herman Mankiewicz, who wrote the original film script. He also recently resigned as president of National Public Radio and goes to work July 5 for the Gray & Co. public relations firm--as a name Democrat in a Republican camp.

Mankiewicz, once Robert F. Kennedy's press secretary, was a party conversation piece, with Nancy Dickerson and others congratulating him. How did he feel about the career change?

"Great. I love it. I think Bob Gray and I are going to be the team of the '80s. Gray & Company is a first-class organization." As for the switch from mainstream journalism, "I'm not sure there's much difference between the two," he said. Laughing, he added, "I have a lot of friends on both sides."

He also didn't seem too worried about his old stomping ground, NPR, even though there are reports an audit may find that financial troubles are worse than originally expected. "I don't know anything about it the audit ; I haven't been involved . . . as far as the auditing is involved."

Guests paid $50 a ticket to see the film at the Sidwell Friends School art center and then join in an after-show reception at the home of Jim and Kate Lehrer (he of PBS' MacNeil-Lehrer Report).

Before the showing, people waited in the lobby and the small cliques dispersed when Ethel Kennedy arrived with son and daughter-in-law Michael and Vicki Gifford Kennedy. Joining Ethel Kennedy, dressed in a long white gown with pink and green lace flowers, was Edwin Guthman, RFK awards chairman.

"I think Frank deserves what he gets . . . and I mean that in a nice way," Ethel Kennedy said when asked about Mankiewicz's move to a GOP stronghold. "Frank is a wonderful man."

And then it was showtime. Mankiewicz opened with, "I don't see a whole lot of clients here," and then continued with recollections of his childhood, sprinkling his remarks with anecdotes about Orson Welles (who co-wrote the screenplay and directed and starred in the film) eating breakfast over a pound of bacon and a dozen eggs.

He talked about the film's history, about its being based on William Randolph Hearst, and how his father loved to discuss the story with dinner guests, how when "we'd have people over for dinner I'd think, 'Great, they're going to talk about that again. I'll get some homework done.' "

Asked if Rosebud, an enigmatic symbol in "Kane," meant anything special to him, Mankiewicz said softly, "To me, Rosebud has always meant a sled. Somebody gave my father one when the movie first came out."

After the film, everyone caravaned over to the Lehrers' home, where people munched on spinach-filled mushrooms and chatted about movies and the RFK Awards.