The American democracy is alive and moderately well, according to a two-hour documentary, "American Journey," that airs tonight on PBS (Channel 26 at 8), a conclusion arrived at after journalist Richard Reeves traveled more than 18,000 miles interviewing everyone from teen-age disco singers to an Alaskan disc jockey.

The film is based on Reeves' 1982 book of the same name, which was an attempt to retrace Alexis de Tocqueville's 1831 journey into the then-wilds of a new nation. De Tocqueville's "Democracy in America" is "the best book that's ever been written about us," says Reeves in the opening scenes, and his effort is "to see how the Great Experiment works now."

The result is an ambitious, commendably unsentimental film. The photography often is beautiful and original, the choice of subjects goes intelligently beyond the stock characters of small towns and large ghettos, and while Reeves' overall view is infused with liberal guilt, it is never unfair. Perhaps the problem the show has lies in the medium itself.

If a picture is worth 1,000 words, then two hours of television probably would be the equivalent of a library. But it isn't. While de Tocqueville could write an extraordinary book that described one uniquely perceptive man's view of a wild new country, a two-hour film that tries to encompass the entire country is inevitably going to lose focus.

A southern black dentist talking about racism is supplanted by black teen-agers in Detroit dancing at their high school prom, and then a black photographer, shown at work and delivering his thoughts about racism. Suddenly the scene switches to Los Angeles and singer Dionne Warwick. "I'm not so bad to have as a neighbor . . . " she says. Then a former chairman of Warner Brothers is walking on the beach with Reeves and talking about how great this country is because only profits--not the government--influence the artistic choices in show business. Why him?

One of the more effective sequences deals with the plight of Haitian refugees, which pointedly follows a sequence on early immigration. The Haitians are photographed as corpses on a Florida beach and as broken-spirited detainees in Miami's Camp Krome. "These images don't fit with American rhetoric," Reeves notes, and yet in fairness allows a government spokesman to make her case with some eloquence. "We will probably have to really tighten up our immigration policies," she says. ". . . But how do we abandon our Statue of Liberty persona?"

The one patronizing sequence concerns senior citizens in St. Petersburg, Fla., shown playing softball--in slow motion with saccharine music. The players, Reeves states baldly, have "outlived their usefulness," and director Malcolm Clarke chose footage that concentrates on self-consciously poignant scenes, like two old ladies dancing together on a neon-lit hotel veranda, and an old man staring disconsolately into the cosmos.

Reeves' conclusion is that "democracy works--for most of us, most of the time," but watching the show, it sometimes is difficult to see whom it is working for. Racism, unemployment, the treatment of American Indians, greed--none of these warts are obscured. But where are the good parts?

It is clear the creators of "American Journey" wanted to avoid jingoism and simple-minded commercial Americana. But they may have gone too far.

The final scenes, for example, are filmed in the farthest outpost of Alaska: Bethel. There one man made a fortune charging new settlers $700 a month for lodgings made of old packing crates perched on oil drums. Reeves states this with a tone of disapproval, another example of American greed. But wait--couldn't this hardy entrepreneur also be viewed as brilliant? Someone else might have just burned the packing crates. The American character is not just to survive, but to imagine prosperity.