A test began yesterday to determine whether downtown Washington will soon get a new tourist attraction--and an appealing new architectural embellishment in the bargain.

When it was built a couple of years ago, the Western Plaza on Pennsylvania Avenue represented one third of architect Robert Venturi's original design. A lot of the negative criticism the place has received since then--it's too big, too flat and too hot, the critics say--is due to this fact.

Yesterday a few of the powerful people who will determine future changes, if any, in the design got a chance to look at a second part of Venturi's scheme, namely a 22-foot-high plywood model of the Capitol and a simple "model" of the White House (actually, just two plywood panels propped up to incidate size) set on the flat terrace of the plaza exactly where he envisioned them in the first place.

Their verdict still is out on the proposal to build the models in stone and make them a permanent part of the plaza, which occupies a unique site in the middle of Pennsylvania Avenue between the National Theatre and the District Building. As J. Carter Brown, chairman of the Fine Arts Commission, said, "I'll have to think about this for a while." The temporary models will be taken down tomorrow, and the round of meetings on the subject will begin next month.

But it took tourists and passersby no time at all to demonstrate their reactions. Even while Brown and others (including architect of the Capitol George M. White and Helen M. Scharf, chairperson of the National Capital Planning Commission) were discussing the idea with Venturi, a group of Japanese tourists snapped about a hundred photographs of the intriguing view, with the model of the Capitol in the foreground and the real thing in the hazy distance.

This spontaneous play continued without letup through the morning. A young photographer, looking to be about 9 or 10, insisted that her parents pose in front of the Capitol model. A young woman, seeking shade, nestled herself into one corner of the structure while a young man, seeking the opposite, propped himself against another of the model's walls for a midmorning dose of sun.

In other words, with the public the models were an immediate hit. These voices won't be heard when the arguing begins again on this much-argued project, but they should be. For a lot of reasons the models improve a place that, even without them, is one of the more extraordinary public open spaces in the country, and the passersby seemed to recognize this immediately.

In Venturi's original proposal the models were the second of three main design elements that subtly corresponded to three different, readily perceptible levels of scale that exist in this particular place.

The flat terrace, with its map of the core of the Charles Pierre L'Enfant's Washington plan reproduced upon its stone surface and its precision-incised verbal messages concerning visions for and about the history of the capital city, beautifully responds to the immediate, close-up needs of users for the plaza.

Unlike so many other things today, the plaza is beautifully made, and it is a wonderfully entertaining, and is even an elevating place to walk and think about this city and its past, present and future. Much of the harsher criticism of the plaza, I suspect, is made by people who only drive by it. Walking there provides an entirely different perspective. The plaza is flat by good design: It was intended to be, and is, a spacious counterpoint to the terraced green of Pershing Park across 14th Street.

Western Plaza also is situated near the end of the grand Baroque vista of the avenue connecting the Capitol and the Treasury Building (which, at the insistence of Andrew Jackson, interrupted the symbolic symmetry of L'Enfant's plan to visually link the Capitol and the president's house). To respond to this scale, Venturi proposed two 85-foot-high stone pylons, framing the view, but these were unmercifully scuttled in the heat of the design fight three years ago.

So too were the White House and Capitol models, which Venturi saw as a necessary, intermediate scale between the great Baroque plan and the close-up view. Justifiable disappointment with the flatness of the place led the Pennsylvania Avenue Development Corp. to reconsider this part of the plan: hence the temporary display of the models this week.

Construction of the models will be considered at the July meeting of the advisory committee to the PADC and, perhaps, by the full PADC board, after which they still face the hurdles of the Fine Arts Commission and the National Capital Planning Commission.

One hopes that this time around they receive prompt approval, and without any nit-picking changes in design, because they look great. Even at first glance the Capitol model establishes a sense of place, becoming an immediate marker for the open area. Then, as one moves in and looks at it from different points of view, it becomes a dynamic element in the space, something by which one intuitively measures distances, be they vast (from the plaza to the Capitol, for instance) or close-in (for example, from one end of the plaza to the other).

And then the models are symbolically apt: the right things in the right places. Situated at the appropriate spots on the L'Enfant map, they restore, in minor key, the connection that he intended and Andrew Jackson spoiled. The pylons ought to be built, too, but that is another story.