If a project promises to look like a city, feel like a city, smell like a city, and act like a city, then it may well become a city. Or at least part of one.

This was my first reaction to Carlyle, a mixed-use development proposal adjacent to Old Town Alexandria.

After a lot of hard and thoughtful work, the developer -- a joint venture of the Oliver T. Carr Co. and Norfolk Southern Corp. -- and the city government, supported by a fair number of residents, have reached agreement about a new quarter in a historic city.

The Alexandria City Council recently approved the Carlyle proposal on a 76-acre site occupied by railroad yards and industrial buildings.

The parcel, just inside the Capital Beltway, is bounded by Duke Street, Hoof's Run, Eisenhower Avenue and Metro tracks.

The site, with two Metro stations within walking distance, is is well-served by public transportation.

When Carlyle is finished, Alexandria will have dozens of new buildings on more than a dozen new blocks with these features:

About 2.7 million square feet of office space and 378,000 square feet of retail space.

Thousands of housing units -- apartments and attached housing -- adding up to 3.1 million square feet of space, some of which will be moderately priced, plus 300,000 square feet of hotel space.

A day-care center, a regional theater and a federal courthouse.

A nine-acre park, several public squares and gardens and landscaped public streets.

Thousands of parking spaces, mostly in garages under buildings, and along street curbs.

More than 25 acres, a third of the site, will be usable open space while 17.6 acres will be dedicated to public streets.

These numbers convey some idea of the project's size -- even higher densities could be achieved using existing, matter-of-right zoning -- but the quality of the proposal and the process it embodies are much more important than its quantitative scope.

Carlyle represents a significant, positive step in the evolution of urban design theory and practice, public land use policy and entrepreneurial initiative.

For once, a collaborative rather than adversarial effort by all concerned parties, public and private, yielded visionary consensus, not wishy-washy compromise.

This happened because the intentions were mutual: Build more city and build it well.

The developer's urban design consultant, Cooper, Robertson & Partners of New York, working with the city's planning commission and staff, accomplished something that American municipalities have been unwilling to do for a long time.

They put aside conventional zoning regulations that so often isolate land uses, offer minimal design guidance and say little or nothing about the shape of the public realm.

Instead they have created a new kind of zoning in the form of a site-specific deal full of regulatory conditions, design guidelines and graphic plans that describe and mandate precisely how an urban district will be configured.

And the deal is not fated to be short-lived or dependent on who owns the property or holds public office. The Alexandria City Council's approval of Carlyle creates a permanent charter, a design covenant that "runs with the land" no matter who develops it.

The Cooper, Robertson design is everything that places such as Rosslyn, Crystal City and Tysons Corner are not -- rationally arranged, street-oriented, pedestrian-friendly, integrative and inclusive. It is a neo-traditional plan, to borrow today's phraseology, in its use of historic, occasionally baroque cityscape concepts: a legible pattern of streets and boulevards, axial vistas, enclosed circles, courtyards and plazas.

The most essential characteristics of the Carlyle plan are simultaneously visual and functional:

The overall street and block geometry, like Old Town, is a simple grid modified circumstantially at its edges. Blocks are similar in size and proportion to Old Town blocks, so that the street fabric of Carlyle recalls and extends Old Town's fabric. Street widths are not excessive -- frequently two driving lanes, curbside parking, and 14-foot sidewalks.

Buildings of varying heights, from 40 to 200 feet, line the streets to create continuous street "walls" that define public open space.

Streets and open spaces also are lined with trees. The design code specifically locates and enumerates street tree quantities, species, and sizes, along with other plantings.

The approved plans have mandatory, block-by-block requirements governing architectural design -- placement of lobby and parking entrances, building heights and setbacks, and facade composition -- for each of the 16 blocks.

Masonry must predominate, there must be no all-glass curtain walls and intermediate heights must be expressed architecturally on facades at different levels. Arcades and interior courtyards are prescribed for certain locations, as are landmark towers and pavilions. However, no architectural styles are mandated in the plan.

Uses of buildings are specifically allocated throughout the site, with most of the residential buildings located in the eastern half near the park. Retail space is concentrated along a major shopping street and retail square in the north half of the project closest to Duke Street.

The locations of special uses -- the day-care center, hotel, health club, performing arts building and courthouse -- are also shown.

Parking is distributed throughout all of the blocks to disperse traffic. Parking garage facades cannot abut streets, but curbside parking is encouraged. Thus, automobiles are accommodated without sacrificing pedestrian street life.

Accompanying the plans are numerous conditions imposed by the city, including provisions for developer contributions and exaction fees, public facilities construction and maintenance, and design review of individual projects by an independent panel of city officials, citizens and design experts.

As the project proceeds, plan amendments undoubtedly will be requested by developers and granted by the city council, most probably concerning the allocation of commercial and residential space, the most vulnerable component of the Carlyle plan.

Indeed, the approved plan spells out the procedure and criteria for such plan amendments.

But generally the plan should remain inviolate, in need only of minor refinements to reflect changing market conditions.

No matter what the final mix of uses and the inevitable fine-tuning yet to come, Alexandria has wisely sanctioned a durable, understandable, compelling urban design.

Assuming everyone sticks with it, the ultimate payoff will be a coherent cityscape transcending the architecture and occupancy of individual buildings that give it shape. And it will put to shame the usual approach to land use regulation -- zoning.

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