When Jim Lehrer took the microphone last night at a party celebrating his 10-year union with Robert MacNeil, he listed a starry bunch of other famous couples.

"Abbott and Costello worked together 19 years. So did Fibber McGee and Molly. Huntley and Brinkley were together for 14 years, Tom and Jerry for seven years and Fred Astaire and Ginger Rogers for only six years," said Lehrer, as his eyes glanced over the crowd in the National Building Museum. He paused briefly and then said, to a few howls, "and Bill Kurtis and Phyllis George for six days."

Standing by was Charles L. Brown, the chairman of AT&T, whose cartoon namesake, despite having just celebrated 25 years with Lucy, was not included in Lehrer's list.

Last night's attention was devoted solely to the journalistic duo who anchor "The MacNeil/Lehrer NewsHour," which airs Mondays through Fridays on Channels 26 and 32, and their show, which is watched by 12 million people a week. Brown was there not only as the host of the celebration and the corporate benefactor -- AT&T has given the program $40 million in the last three years of its five-year association with it -- but also as a former interview subject.

"I didn't get any breaks nor any bruises," said Brown, who has made it to the interviewing table twice. Joining him were dozens of alumni of the steely questioning who fell into three categories of MacNeil/Lehrer veterans.

Among the enthusiastic alumni were Sen. Alan Simpson of Wyoming, who said, "I've been on more than any cowboy from Wyoming is entitled to -- eight to 12 times." Like many others, Simpson enjoyed the longer interviews the show offers. "It is most effective because of the time. It is hard to watch an issue that you have worked your butt off on done in 90 seconds."

Other former guests, as disparate as Patrick Buchanan, the White House director of communications, and Ralph Nader, the country's best known consumer advocate, had wry assessments. Said Buchanan: "Well, it is different from 'Crossfire,' which was 'MacNeil/Lehrer' without the gloves. But they do a fair job. It is quality TV. Even Mr. Nixon likes it." When asked his appearance tally, Nader quipped, "Not enough. My quota is about once a year . . . and do you know why? Because I have the potential of reaching out and touching."

Then there were the loyal watchers who hadn't made it to guest status. One was George Stevens Jr., the founder of the American Film Institute. "If there is an important story, I know there will be real substance, from the summit to the baseball strike," he said.

Also congratulating MacNeil and Lehrer were Sonia Landau, the chairman of the Corporation for Public Broadcasting Board, M. Carl Holman, the president of the National Urban Coalition, Rep. Timothy Wirth, (D-Colo.), Roger Stevens, chairman of the Kennedy Center, Joan Claybrook, attorney Vernon Jordon, Frank Mankiewicz, vice president of Gray and Co., and a slew of network correspondents. And getting almost as much attention as MacNeil and Lehrer were the show's chief correspondents, Charlayne Hunter-Gault and Judy Woodruff.

Earlier in the day MacNeil, 54, with 30 years of interviews under his belt, and Lehrer, 51, with nearly as many himself, sat in Lehrer's Shirlington office, replete with its collection of bus company signs, and talked about the meat and potatoes of their longevity . . . the guests.

In February MacNeil interviewed Cuban President Fidel Castro. "It was classic. It had preparation, follow-up. Of course, he interviewed him for eight days," said Lehrer. MacNeil laughed and joined in, "I said to Daniel Ortega the other day . . . it went on for 4 1/2 hours, and Ortega laughed, and then I said 'Yes, that was only two questions,' and he really laughed." The Cuban president, who had put MacNeil under house arrest in 1962 when the correspondent worked for NBC, showed the interview on Cuban television. "It contains quite a few questions you would assume he wouldn't want aired. Like, 'Why wouldn't you tell the people how many of your troops are killed in Angola?' " said MacNeil.

One of the professional nonspeakers Lehrer remembers was Nelson Rockefeller. When Rockefeller was vice president and the 1976 primary season was heating up, Lehrer tried in vain to get him to talk about candidate Ronald Reagan's criticism of Jerry Ford. Afterward, Lehrer recalls saying, " 'Mr. Vice President, you didn't say much.' And he said, 'I didn't come here to say anything. They blamed me for Goldwater losing, Nixon losing, and they aren't going to blame me for anybody losing again.' So I said, 'I had these questions.' And he said, 'I didn't get to be where I am answering questions just because somebody like you asked them.' "

Then there was Lehrer's nonduel with the late Frank E. Fitzsimmons, president of the Teamsters union. "I asked him a question and he reached in his pocket and pulled out a paper and he just started reading. Now what do I do? Do I grab the paper? It was awful. I ended up only asking him two questions in about four or five minutes because he wouldn't shut up."

Both said they get special pleasure interviewing people who are not front-page stories, such as MacNeil's discussion this week with a customs agent about art thievery and Lehrer's interview with a woman who had been in Mexico City during the earthquake. But they agreed on the show's finest period.

" The time I felt we really had it, we were on to the right thing and were doing it the right way and there was an audience for it and there always would be, was during the Iranian hostage crisis, which we covered better than anybody in broadcast journalism.

"Not by having cameras in front of the embassy in Tehran but back here with people who understood what was going on. Many U.S. senators -- and this is not to blow our own horn -- told us they ran to their television sets every night to find out who was this guy Khomeini," said Lehrer. MacNeil, who interviewed Khomeini while the Moslem leader was still in exile in France, concurred. "Anyone who watched our program consistently would not have been surprised that the shah was overthrown."

Their best stories recently, they said, have been on the problems of American farmers, on the Philippines and on South Africa.

In addition to the professional satisfactions of news scoops and discussions with people who make a difference, they said the success of the show is based on their own chemistry built on a friendship and respect "very rare in a business like this."

"The personal exposure and ego involved breeds personal competition," said MacNeil. "It almost inevitably involves at some time making your career at the expense of someone else's.

"We have known that neither one of us is going to do something at the expense of the other, whether by accident or design," Lehrer said. "In a business where enhancement of one's self can sometimes be seen as everything, this is truly a rare thing. It boils down to trust."

MacNeil feels the public can sense that lack of ego-clash in their nightly appearances. "It permits us to do a program where our personalities aren't the principal commodity."

What about those professional critics who find them dull?

That hurts, said Lehrer, but there are compensations.

"We started off saying to ourselves 10 years ago that it is fairly easy to produce heat, but very tough to produce light . . . Sometimes we are criticized for . . . taking the passion out of issues," Lehrer said. "But if I am going to fail, I would rather do it that way."