"I want to welcome you all to Washington, D.C.," said comedian Mark Russell, "home of your federal government -- 2.9 million people doing badly that which need not be done at all."

The conventioneers visiting from Cleveland to Coral Gables roared and placed a check in the "excellent" column next to Russell's name on their scorecards.

"We are often accused in Washington," Russell went on, "of being out of touch with what goes on in the rest of the nation. That was the crux of Jimmy Carter's 1976 campaign. Carter's theme in '76 was 'Washington is rotten to the core, and I want to go there.'

"Now, four years later, he's the guy he warned us about.

"Voltaire once said, I think it was on the Dinah Shore show, 'i may disagree with what you say, but I will defend with my life, my right to tell you to sit down and shut up.'"

But the audience, now sitting though its 12th speech of the day, might have disagreed. They came, to what is perhaps the talking capital of the world, for the International Platform Association's annual convention -- a five-day gab session featuring the best of the American lecture circuit.

In the Hyatt Regency the delegates from colleges and civic clubs sat sampling the speakers' foods with the intention of lining up the best for gigs back home.

And while most of the speakers who took the podium yesterday were hoping to make audiences, and honorariums, appear before them, there were at least two who have worked to make people disappear.

On the dais, G. Gorden Liddy said he would not have objected to the disappearence of columnist Jack Anderson, and would have volunteered to "break every law in Germany" to assassinate Hitler in the late 1930s. A few speakers later, magician Harry Blackstone Jr. was introduced "as having made more people appear, reappear and disappear than any other man in history".

"There were times," said G. Gorden Liddy, the stoic, silent man of Watergate "when I was sitting there listening to John Dean's selective memory and it would have been nice to say, 'hey, wait a minute Charley, let's cutout the bull ----.'"

Following a performance by Martha Faye, world-champion frisbee-catching dog, Liddy, in chatty fashion, warned the audience of "America's Last Chance" and encouraged questions: "You've been waiting eight years to ask me some questions, and I came to play. I'm perfectly safe. I'm unarmed."

He said that by avoiding "pleasant realities" such as Soviet military prowess or the work of the CIA with an "I-don't-want-to-talk-about-it attitude," America has endangered its national security. The audience listened intently.

"the world is not a nice neighborhood," Libby continued. "It isn't Grosse Pointe. It isn't San Diego.It is a very dangerous neighborhood at about 2:30 in the morning.

"If you want to go on swimming in that ocean," said Liddy, "you better not think it's Charlie the Tuna out there, because it's not -- it's Jaws. And you're going to get eaten."

During the question-and-answer perioda women stepped up to the mike and said, "I'm from Louisiana and reality is even more distorted there." Liddy responded incredulously. "More distorted than Washington?" he exclaimed. "Here we think we can withould the onslaught of Soviet panzers by refusing to turn on the lights of Cristmas trees."

Later, Blackstone, aprofessional distorter of reality, cajoled doubting spectators to believe in an imaginary deck of cards. He also made birds disappear, guesssed the right card and lifted the watch of a man he brought onstage to help with his act.

"Can I leave my wallet with my wife?" asked one hastily drafted assistant as he climbed onstage.

Blackstone's wife and full-time assistant, Gay Blackstone (blond but no black tights), also spoke about reality."For instance, when I'm lying there and the 36-inch buzz saw is coming at meand I can see the blade, that really is dangerous."

But the magician himself, who had just received the IPA'S first Harry Blackstone award, named after his father, was less interested in reality. Snapping a deck of cards from nowhere, he proclaimed, "That's where the imagination and reality become one."

After the show, and a standing ovation from the seasoned audience, Blackstone said, "I feel there is enough reality already. We need to have a little more fantasy, but as an entertainment force. We already have enough fantasy in our politics."

Earlier, Frank Vogl, British economist and Times of London correspondent, delivered a speech appropriate perhaps for local Optimists' Clubs. Titled "America's Bright Economic Future," Vogl's talk began with the qualification, "I do not wear rose-tinted spectacles and view America solely in golden colors.

"Often Americans look inward, excluding the global environment, and at such times Americans forget how well off they are." He then suggested, "If you want to see bleakness, try shopping in East Germany sometime." And he told of British trade union strength, which kept him on strike for a year, during which he was paid full salary and received a 47-percent productivity raise.

Diversity, according to Dan Moore, IPA general director, is vital to keeping a lecture audience happy.

"It's a throwback to the old days of the Chautauquas, which was really a traveling show that came into town and was the entertainment for a week," said Moore. "They'd have somebody like Teddy Roosevelt along with circus acts. You couldn't have too many serious speeches all at once."

But the days of the Chautauquas eventually were doomed by the diverse entertainment offered by radio, movies and the automobile.

Ironically, it was television that boosted the lecture circuit so that Henry Kissinger can earn $18,000 plus expenses for a night's talk.

"What they didn't count on with television," said Moore happily, "was that seeing a man like Hugh Downs on TV every morning creates an appetite to see that man across the dinner table at your club."

But Russell was less optimistic. "It's a dying art," he said of platform speaking. "These are the last people on earth who talk in complete sentences. sIn 20 years everybody will talk like a top-40 disc jockey."