Of all the one-man shows that have been trotted out over the past two decades, "Will Rogers' U.S.A.," which opened a three-week run last night at Ford's Theatre, is no doubt the most congenial. Like the personality of the cowboy philosopher it celebrates, this two-hour entertainment is as unpretentious and easy-going as a chat over the back fence.

The source of Rogers' endless fascination was the American politician, but he took after him with good-natured amazement, never scorn. He didn't claim to be a know-it-all. In fact, he pretended to know nothing at all, "only what I read in the newspapers." But he had eyes and common sense, just like any other American. As a result, he didn't talk up to his audiences or down to them. He talked to them and before long a kinship was born.

It's just what actor James Whitmore does at Ford's. Moseying out onto the stage, taking in the crowd with pleasure and treating himself to a stick of gum before moving on to the chatter, Whitmore suggests he has all the time in the world to strike up a friendship. Nobody's trying to impress anybody here. The anecdotes will come, when they come. So will the laughs. Getting comfortable with one another first is just as important. Never was a one-man show seemingly so content to play the lay of the land.

Whitmore is an acknowledged pro at historical impersonations -- in his repertoire, he also has one-man shows about Harry Truman and Teddy Roosevelt -- but I don't think I'm imagining things to say that his heart belongs to Rogers. The performance has long since become second nature, which doesn't mean that it isn't as freshly observed as it always was. It means simply that any trace of effort disappeared years ago. The actor's art is all but invisible. Although Whitmore has already performed "Will Rogers' U.S.A." three times at Ford's, a fourth engagement doesn't really seem like overkill. Who wouldn't welcome an old neighbor back into the block?

The material, neatly woven together by Paul Shyre, certainly hasn't gone out of date -- maybe because politicians themselves resolutely refuse to change. They're still enacting dumb laws on the Hill, senators are still making interminable speeches (while others are dozing off), and congressmen are still known to be caught with their hands in the till. In fact, you may swear the script was written last month in Dallas, when Whitmore asks, "Why do they pray so much at those conventions?" (Answer: "I guess they're asking for forgiveness for what they're about to do.")

Politics is the leitmotif, but the script also permits Rogers to talk about the west as it used to be, do a few rope tricks (badly), impersonate Calvin Coolidge and choke up over the memories of the gallant pony that was the Rogers' family pet for 19 years. Some of the sentiments could be sticky if the actor gave in to them. Instead, Whitmore goes against the grain, apologizing for his little lapses of emotion and therein implying that Rogers is no different from the rest of us.

He was, of course. He was one of the most popular, influential and wealthy entertainers of his day. But he always gave the appearance of being the last to know it. Modest, affable and wise, "Will Rogers' U.S.A." is also our most democratic one-man show.

WILL ROGERS' U.S.A. Adapted and directed by Paul Shyre. With James Whitmore. At Ford's Theatre through Sept. 30.