The people usually in the know weren't last night. At least for a while.

Most of the 100 or so journalists attending a reception honoring Paul Duke for his 10-year reign as moderator of "Washington Week in Review" had left their newsrooms early. So early, in fact, that word of Labor Secretary Raymond Donovan's indictment hadn't yet reached them.

"Oh, my God," gasped Eileen Shanahan of Medill News Service and a frequent panelist on the news-analysis program.

Duke, on the other hand, wasn't caught off guard. "News travels fast, especially where newsmen are." Pausing a moment, he added, "If he's been indicted, that's obviously something we'll deal with on this week's show."

The atmosphere at the Decatur House was like a class reunion for program alumni and Ford Motor Co. VIPs, who were on hand to celebrate their fifth year as the show's underwriters, as well as to share in Duke's anniversary.

Philip Caldwell, Ford's board chairman, presented Duke with a pair of gold cuff links, tiny replicas of 1903 Fords with ruby headlights. Caldwell made some remarks before handing over the cuff links to Duke, and he got the crowd laughing. "Well, President Reagan was in our city today," Caldwell said, referring to Detroit, "so I know all about cue cards. Now I'm looking for the teleprompter. I really want to do it first class, he Reagan sure knows how to."

Jack Nelson, with the Los Angeles Times for 20 years, is a regular on the show and says his wife claims he would "kill to be on it."

Nelson, like other panelists, recounted tales of audience feedback. "You get quite a bit of hate mail. Lately I get a lot of mail saying, 'Quit beating up on Mondale.' I used to get a lot of mail saying the same about Reagan."

Duke also reminisced about some of the mail that's crossed his desk. "We get a lot of mail, some of it flattering, some of it not." And he proceeded to tell of one letter writer from Kalamazoo, Mich., who complained that the show had "too much gloom and doom and he wondered what the suicide rate was each week after we went off the air."

Another man wrote in saying that he and his bride were planning on honeymooning in Greece. Duke, shrugging his shoulders, said they wrote back that it "was a great idea."

The program, which is estimated to reach 7 million viewers weekly, is carried on almost all of the nation's 292 Public Broadcasting Service stations.

Charles Corddry of the Baltimore Sun has been on the show since 1967, the year the show started. Corddry's most memorable moment on the program was when "I predicted that Sadat would never go to Jerusalem."

Laughing, he said, "How could I know Walter Cronkite would publicly invite him?"