Giving new life and new form to Washington's Potomac and Anacostia River waterfronts is in all respects a fabulous prospect, not to mention a monumental effort that is long overdue.

Even if only some of what is proposed comes to pass, the city will be positively and dramatically transformed.

The most recent proposals envision a $400 million major league baseball stadium and a professional soccer stadium. Bracketing the Anacostia River near the South Capital Street Bridge, these two sports facilities would enrich the diverse ideas and uses -- commercial, cultural, residential, recreational -- included in the city's justifiably ambitious Anacostia Waterfront Initiative.

The initiative encompasses the Southeast Federal Center, adjacent to the Washington Navy Yard, where new development is well underway; the underused parkland of Poplar Point across the river; and other Anacostia and Potomac River frontages, including the Southwest Waterfront, where a makeover is envisioned.

Farther up the Potomac, District and National Park Service plans call for redesign of the waterfronts at the Kennedy Center and Georgetown, adjacent to the Whitehurst Freeway. That road eventually should be taken down and replaced with a well-designed waterfront boulevard.

For years, we have talked about how Washington's rivers could serve local transportation needs, with water taxis plying the Potomac and Anacostia.

Thus we can foresee in the not-so-distant future a city finally connected -- intimately, actively and at an appropriate scale -- to its cleaned-up, increasingly animated rivers. Indeed, Washington's rivers and their embankments should be as vital to the form, life and culture of the city as the National Mall.

If he could see Washington today, Pierre L'Enfant, who planned the new American capital more than 200 years ago, assuredly would agree.

That brings me to France. L'Enfant was familiar with and clearly influenced by 18th century baroque city-planning principles and motifs characterizing French landscape design, most evident at Versailles. L'Enfant, Thomas Jefferson and their 19th century successors who continued planning Washington also saw Paris as a model. They admired its consistent, low-rise building fabric, its ceremonial avenues and public squares, its grand civic edifices, its parks and its integral relationship with the Seine River.

Paris and its river still have lessons to teach Washington. While there this summer, I had the pleasure of visiting "Paris-Plage" -- the city's Seine River beach.

The Seine River, unlike Washington's rivers, is lined not by gently sloping parkland or steep palisades, but rather by stepped, structural embankments, stone retaining walls and linear terraces, with the city's primary street level elevated 20 to 30 feet above the river.

City streets run parallel to the river along the tops of the terraced embankments and connect to the many bridges crossing the Seine. Lining these streets are river-fronting buildings containing offices, shops, apartments and restaurants. But there are also high-speed expressways, similar to Rock Creek Parkway, running along the lowest embankment levels, passing under the bridge arches next to bridge abutments or sometimes through tunnels within embankments.

The Paris-Plage program transformed about two miles of the Seine's right bank (north side), at the heart of the city, into an urban beach. The premise is simple: Many Parisians cannot afford to vacation on the beaches of the Cote d'Azur. Therefore, asked the mayor, why not bring the beach to Paris?

For one month, from July 21 to August 21, the city closed the high-speed expressway -- despite objections from Parisian motorists -- and brought in 3,000 tons of sand to create a "beach" atop the paving.

Enhancing the beach ambience were potted palm trees, flowers, beach furniture, hammocks, a heated swimming pool, a concert stage, wooden decks and grassed areas, multiple petanque (a French bowling game) courts and numerous temporary cafes.

Paris-Plage reportedly drew 200,000 daily visitors, seven days a week, from 8 a.m. to midnight. The effort required months of planning but cost the city only a little over $ 700,000, with another $ 1.7 million paid by corporate sponsors.

The idea has been so successful that it has been replicated elsewhere, in other European cities blessed with rivers -- Lyon, Toulouse, Berlin, Brussels, Budapest, Milan.

Yet the lesson of Paris-Plage for Washington is not that we need an ersatz beach. Washington's rivers already have enough real, grass-covered beaches, not to mention the reasonably affordable, nearby Atlantic beaches.

Rather, Paris shows that urban rivers and their structured edges can be extraordinary places for intense activity. Although riverfront activities can happen spontaneously through private initiatives, they also can be publicly programmed with great success.

Most important, Paris illustrates the value of bringing the city -- both buildings and streets -- right to the river's edge, and the importance of designing river edges to accommodate varying uses.

These lessons are essential for Washington's next phase of development, especially because many people tend to believe that the city's rivers should all be bordered by grass-covered parks. We don't need more shoreline parks.

The still-evolving waterfronts in Georgetown, Southwest and Southeast offer a last opportunity to creatively redesign and build urbanized, invigorated Potomac and Anacostia River embankments with promenades and plazas, restaurants, shops, apartments and offices.

Washington isn't Paris, but Paris and its river are still wonderful models.

Roger K. Lewis is a practicing architect and a professor of architecture at the University of Maryland.