Watergate it isn't, but the briefing-book caper is still the best story in town. In terms of genuine excitement, it's the only story in town.

The recent Supreme Court decisions--on tuition and taxes and on the congressional veto--are far more important than the long- ago theft of Jimmy's Carter's debate pony. They are also far less interesting.

El Salvador, in terms of both foreign-relations principle and domestic interest, is a worse loser than Vietnam; the American economy is in the doldrums, no longer frightening but not yet exciting; the Democratic bid for the presidency features candidates whose names might be Tweedle-Ho and Tweedle-Hum.

The briefing-book thing, though, is tonic for a whole range of Washingtonians. It provides a wonderful opportunity for columnists, uninvolved politicians and other commentators to wax sanctimonious about the ethical implications of accepting stolen documents. (Too bad Eric Sevareid has retired. I can see him now, head tilted forward, eye looking up into the camera, vouchsafing some carefully balanced quasi-profundity: "The briefing book affair is no Watergate, but, then, neither is it a mere prank, to be ignored as political-as-usual.")

It contains enough ethical meat to provide a feast for those who knew all along that Democrats are klutzes, or that Republicans are amoral. It gives outsiders a chance to see powerful insiders act under pressure: will they stonewall? Who will be the sacrifical lamb, and how early in the drama will he be sacrificed?

But most of all, like a good James Bond thriller, it provides excitement without risk --at least without risk to the titillated viewer. Whether the guy who stole the documents is Agent 007 or some sinister operative from C.H.A.O.S. depends on your attitude toward Ronald Reagan and Jimmy Carter. But either way, the drama works: will he be caught? Will his superiors be unmasked? Will the conflicting accounts of the principals be reconciled in a nice, neat finale? Tune in tomoorow.

Tomorrow, of course, is what made Watergate such a great Washington hit. Every day carried the possibility--the expectation--of new revelations, of an ever-tightening noose, of a final, exciting climax. (It wasn't all about hating Nixon; the play was exciting long before we dared think that the cornered villain would be the president himself.)

As happened with Watergate, the briefing-paper caper has already become bigger than the triggering indiscretion, a fact not yet appreciated by those who, like Tip O'Neill, insist on pointing out that Reagan would have won the election with or without the briefing book. Was Watergate less interesting because George McGovern was a certified loser? No one ever knew what the Watergate burglars were looking for, and, after the first few days, nobody cared. The excitement stems not from the foulness of the deed but from the drama of the chase.

The thing is fun, and promises to become more so, unless someone with no sense of drama starts to direct the show. The worst thing that could happen, from the audience's point of view, is for two or three credible figures to stand up and say: "I took the book, and here's how I did it; I passed it along, and here's how we used it."

It would make terrible drama. And this is the only decent play in town.