The Washington show is back at last.

"Washington: Symbol and City," at the National Building Museum, reopens today in a new and improved version after three years of downtime.

It's a really good show, the kind you can take your mother to, or friends from out of town, so they can acquire in a reasonable time a fair understanding of the peculiar dynamics of their capital city. Less than an hour will do the job, although for Washington history buffs, more than an hour will be amply repaid.

The exhibition originally opened in 1991 and was closed in 2001 for an overhaul. In the meantime, the City Museum of Washington, a new institution with its own Washington show, opened last year just a few blocks away, raising a serious issue of redundancy.

Not to worry. "Washington: Symbol and City" possesses a compelling story line, something the City Museum's exhibition lacks. (The exhibits there will close in April.)

As its title hints, the Building Museum show has tension at its heart -- tension between the broad diagonal boulevards and the narrower right-angled streets, the national constitution of the democracy and the city's votelessness, the behemoth federal government and weak city administrations, the monumental core of the city and its street-corner neighborhoods.

The list just goes on and on, but basically it boils down to the single, overriding push and pull built into Washington's dual history as glorious national capital and vibrant local city.

This duality is the inescapable theme of Washington life, hard to avoid even if you try. It is almost impossible to travel around the city's neighborhoods without encountering a reminder of the capital's symbolic import -- the poignancy of the Civil War forts, for instance, or the unforgettable constancy of the Washington Monument or Capitol dome on the city's skyline.

The Building Museum exhibition derives its cogency from this theme. Occupying three galleries on the museum's first floor, the exhibition begins with a room devoted to the history of the monumental city -- the L'Enfant plan, the Capitol, the White House, the Mall, the major monuments. This forms the essential background for the rest of the show, which is taken up with compact examinations of particular subjects such as housing, transportation, culture, parks, education and religion.

Truth be told, the presentations often seem too compact, leaving a visitor wanting to see more, learn more. This is greatly preferable to information overload, a common malady among educational exhibitions. The Building Museum show, at the very least, is a great inducement to hit the books or, even better, the city's sidewalks.

Much of the show's impact is due to the excellent selection of materials. It is easy to tell that folks who know the city well were in charge -- the lead curator was architect-historian Don Hawkins, whose knowledge of the city is encyclopedic, and he was assisted by Portia James, curator at the Smithsonian's Anacostia Museum.

Take, for instance, the immensely informative photograph of downtown Washington in the Christmas season of 1948. It is like a novel of Washington life at mid-century.

Observed from a window in the second or third story of a building looking east along F Street NW, the image shows sidewalk crowds that, today, seem almost incredible. Postwar prosperity is at its height. Sleek new cars are beginning to replace the bulkier prewar models, but automobiles must share the roads with streetcars. Downtown was the region's commercial hub. The doorways to the Woodward & Lothrop department store are jammed with people. Small, locally owned, non-chain businesses predominate.

It is an everyday scene that, we now know, would change dramatically in the years to come as downtown, for a potpourri of reasons, lost much of its allure. Half a century later, downtown is staging a remarkable comeback, but, to state the painfully obvious, it'll never be 1948 again.

Nor 1942. There's a tremendous three-minute film on view that vividly demonstrates the amazing influx of "government girls" during World War II.

Nor 1916, when African American teenagers flocked to the newly opened Dunbar High School, which in an era of segregation became nationally renowned for the quality of its faculty and graduates.

Nor, for that matter, 1791. All roads in the Washington story eventually lead back to the amazing Maj. L'Enfant, the visionary Frenchman "who so admired America that he preferred to be called Peter rather than Pierre." The real fruit of L'Enfant's admiration, of course, was his brilliant plan for the new capital city.

As in the original "Symbol and City" exhibition, the two scale models made for the Senate Park Commission in 1901 are featured attractions. These consist of a "before" model showing in great detail how central Washington looked at the beginning of the 20th century, and an "after" model of the dramatic changes the commissioners proposed. Many of these changes were carried out in the following decades, producing the Mall pretty much as we know it today.

Unfortunately, this time around the organizers decided, presumably for lack of space, to show only the central portions of the models, reducing their size by two-thirds and thereby eliminating lots of fascinating detail. Focusing on the Mall is understandable, but even so, slicing and dicing these invaluable artifacts is a great shame.

The remnants are safely stored away, thank goodness. In another decade or so, maybe the museum will come to its senses and put Humpty together again.

Happily, the exhibit organizers did better by the other important models in the show -- detailed renditions of the Capitol, White House and Lincoln and Jefferson memorials constructed by model-maker Rebecca Fuller. Conceived on the same scale, the models are made to be touched, a benefit to the blind and sighted alike.

The presence of the "Symbol and City" exhibition somewhat softens the impact of the City Museum's unhappy announcement that it will close all its exhibitions, including "Washington Perspectives." With its scattershot approach to the historical material, that exhibition, in any case, needs to be rethought.

Washington's history probably is rich enough to sustain two museum exhibitions, but the second would need to be carefully adjusted to the first so they complement each other. As of now, "Symbol and City" definitely is number one.

Washington: Symbol and City will remain on view indefinitely at the National Building Museum, 401 F Street NW, open 10 a.m. to 5 p.m. Monday through Saturday and 11 a.m. to 5 p.m. Sunday. Admission is free.

Models made for the Senate Park Commission show how central Washington looked at the start of the 20th century, right, and commissioners' proposed changes, above, which brought the Mall closer to how it looks today.