One fiasco often breeds another.

The National Visitor Center, alias Washington's Union Station, currently displays an exhibition called "The Streets of Washington," which is as well meant in vague intent and as infuriating in inept execution as the Visitor Center itself.

Most taxpayers in this area are aware that the Union Station fiasco cost $42 million so far, with at least that much more to come to undo some very serious damage.

The vague intent 10 years ago, you may remember, was to save and restore Daniel Burnham's magnificent railroad terminal and to rprovide parking for tourists behind it over the railroad tracks so tourists could do their sightseeing by tourmobile and stop cluttering up Washington's streets with their cars.

Union Station was restored, to be sure, but it also was grievously amputated (the entire east wing) and mutilated (a 50-foot-by-120-foot hole in the center for a noisy, banal slide show). Railroad services were pushed out of the railroad terminal into a sorry, inadequate shed behind it.

The parking garage was never completed (Work on a bad plan was stopped after a $4.9 million cost overrun.)

So now we have no tourists to speak of a diminishing number of discouraged rail passengers who must lug their baggae through all this mess: a dirty carpet; some potted plants; some flags. A few bored information officers with little information: the bad smells of a poorly ventilated fast-food dispensary; and - the latest addition - a show on "The Streets of Washington.

A paragon of deft grantsmanship - no fewer than 11 public agencies contributed, led by the National Endowment for the Arts - this exhibition cost only $611,500 ($211,500 for the show and $400,000 for the "study" on which it was based).

The exhibition consists of a grove of big plywood trees, some park benches and nine giant, black canvas cubes. It was designed by Massimo Vignelli, the industrial designer who gave Washington Metro riders a kink in the neck by lettering the station names vertically on square columns. (Signs are now also on the wall, where you can read them.)

On three sides, according to the press release, the canvas cubes were to be adorned by Venelli's graphics, but he had not gotten around to that.

On the fourth side we are treated to a "continuous" sound-and-slide presentation, each lasting 71/2 minutes. At the time of my visit the other morning only four of the nine worked.

A fifth was finally set in motion thanks to the efforts of Robert Snyder, a flustered young man in the employ of ComCorps Inc., the ourfit in charge of sound-and-slide shows. Snyder explained to his only visitor (me) he had to cope with with "very delicate machinery."

The very delicate machinery produced the same, tedious sort of slide show with multiple slides, single slides, slowly fading slides, double exposure slides, long-drawn-out slides, rhythmically flashing slides, blurred slides and sharply focused slides, we suffered through during a long Bicentennial year.

This one shows that there are people on the streets of Washington. Children hopscotch, climb on statues, run and sit. Women stand, walk, sit on stoops, smile or frown. Men stand, walk, sit on stoops, smile or frown. Some are black, some are white, some are well-dressed, some are poor.

Sometimes the music mercifully fades and you hear voices mumbling wisdoms like: "Sure, man, I dig the street, y'know, I mean, that's where it's at, y'know." The music, mercifully, comes on again.

After 71/2 minutes of standing in the draft of Union Station and inhaling the aroma of hot dogs, hamburgers and chili, you move on to the next black canvas cube: "Streets of the World." More sound, less talk because most of us don't understand Hindi anyway. Othewise it's much the same.

The show on Pennysylvania Avenue has interesting historic views. The avenue was much livelier before the government moved in to make it lively.

But that's about it. The leaflet promises to show us what can be done and how it can be done. But it doesn't - unless architect Joseph Passonneau, who conceived the exhibition, and the supporting agencies, actually believe that slide shows of happy people solve problems and make people happy.

Passoneau's simple message is that we can improve our cites by improving their streets with trees, benches and such, spped automobile traffic and curtail curbside parking.

Fade out.

Where the show ends, the real problem begins, as the District of Columbia's reluctant efforts to reduce suburban parking on D.C. residential streets prove.

Silly, expensive slide shows will not advance Passoneau's solution because it is not solution. If we want to speed and facilitate automobile traffic in the city, we must provide parking. If Passonneau doesn't want curbside parking, he should build parking garages instead of wasting money on slide shows.

The $400,000 "study" on which the slide, show is based is just as fuzzy and misleading as the slides in Vignelli boxes. It tells us that Washington and other cities have spread in the last 100 years, that downtown Washington has run away from the Capitol, that it would be nice if we completed the Metro regional rail system, that streets should be at least as well designed as Pompeii's, that buses carry more people than private cars, and that we should have more trees, side lanes and road bays for bus stops and unloading trucks.

All this has been publicly advanced for half a century or more and is presumably taught in city planning schools.

Rehashing conventonal wisdom is no substitue for action.