Way back in the Sixties, when nostalgia was in its innocent youth, Max Morath staked out a claim to 1890 through 1915. He chose that period because "I have a front-of-the-mouth Vaudeville voice," because "you can't do the music of the Twenties without a band and I don't want to travel with a band - I've tried it," and because nobody else wanted it.

In "Max Morath at the Turn of the Century," which played Ford's Theatre twice in 1970, he explained the phenomona of that time which explains why many Washingtonians are here today: "The government was rapidly expanding to meet the needs of an expanding government." Now he is back at Ford's with "The Ragtime Years," another blend of music, humor, popular history and odd bits of information from the same era.

"What you have then is progress and optimism, ending in disillusionment because of the war," he said. "It was the beginning of everything we call popular culture - the movies, phonographs, mass magazines."

And therefore it is the beginning of documented corn. It is easier to sneer at a period that has left its fleeting moments than at one which bequeaths only its classics. Morath plays against a background of period hand-tinted slides which were made to illustrate popular songs, and are now so thoroughly dated in style and emotional approach that they encourage one to feel that people have progressed since that day.

It is an idea Morath himself squelches. "It's our blind egotism that makes us believe we are absolutely right now, and everyone else was backward; I can't say it more simply than that."

Something of an amateur historian, Morath makes his case with, among other things, the wit-and-wisdom of Finley Peter Dunne's "Mr. Dooley," a great number of women composers of ragtime, the "anything but demagogic oratory" of William Jennings Bryan, and the efficiency of "the extensive, inter-urban, pollution-free mass transit system" called the trolley.

Still, he says, it was a terrible time to live. "Most people didn't do anything but work and die - and watch their children die. And of course, sex wasn't invented until 1915."