A fascinating architectural transformation has taken place at one of Washington's top legal institutions. During the last decade or so, the Georgetown University Law Center has been changed, in stages, from a mega-structure to a campuslike setting, from a solitary '70s box to a family of buildings that relate reasonably well to one another and to the outside world.

The final piece was put in place recently with the completion of an addition to that brick-and-glass '70s cube. This addition merits attention on its own, but its greater significance is as part of a story that began 14 years ago, when the school's administrators first asked the Washington architecture firm Hartman-Cox to evaluate its needs.

Space itself was the most pressing issue. The downtown law school -- kept separate at its founding more than a century ago from the Jesuit campus on the Georgetown heights -- was bursting at the seams. This was a surprise. Enrollment had increased much more than anticipated after the building's dedication in 1971, and every nook and cranny was overstuffed. Some departments were forced to rent elsewhere.

Yet space was hardly the sole problem. The building, designed by Edward Durell Stone at the height of his fame, exhibited fundamental flaws. The organizing idea behind it -- to pack everything a law school needs into a single box -- was suspect. It made for labyrinthine corridors and many cheerless, windowless rooms. In many places the interior finishing of concrete block exuded a bunkerlike feel.

And the exterior image was wrong. Stone was in his abstract temple phase -- he designed the Kennedy Center, with its marble sheathing and attenuated columns, around the same time. Accordingly, he placed his law school building atop a concrete platform on an isolated block on the edge of downtown. This arrangement resulted in some terrible interior spaces -- behind those concrete walls you feel as if you are deep underground. From the outside, the raised building, rather graceless to begin with, looked more like a besieged fortress than an institution devoted (at least in theory) to improving humankind's sorry lot.

McDonough Hall -- a k a the big box -- still stands today on downtown's eastern edge, facing New Jersey Avenue on one side and a burrowed interstate freeway on the other. (The actual address is 600 New Jersey Ave. NW.) But it has been transformed almost beyond recognition, thanks to the skills of Hartman-Cox and the client's persistence (and lots of money donated by alumni and others). Constructed atop the broad entry platform to the east of the building, the addition manages the considerable feat of putting a civil new face on Stone's dour one without altogether upstaging the original.

It is a functional face, to be sure, and not a mere mask. The 45,000 square feet of new interior space provide much-needed new classrooms, conference rooms and offices for both students and faculty. (With nearly 2,800 students, including part-timers and candidates for advanced degrees, Georgetown is one of the largest law schools in the land.) But aesthetics played a major role in the decision to build the $12 million addition. The school wanted a true community of buildings. Within limits, it got what it wanted.

The first Hartman-Cox project was the Edward Bennett Williams Law Library immediately to the north of McDonough Hall. The library grew out of the firm's 1983 report on the school's space needs. Although everybody realized expansion was necessary, the Washington architects rejected the idea of simply adding to the top of Stone's building, which had been constructed to take the load of three more floors. They argued that a separate library building would be superior to a vertical addition in aesthetic, urban design and functional terms.

The result, completed in 1989, certainly proved their points. The architecture is a succinct take on Washington's familiar classicism, and the exterior spaces -- a pleasant arcade on the west side of the McDonough platform and a tree-lined greensward between the two buildings -- gave the school civic breathing room.

Next came the Bernard and Sarah Gewirz Student Center, a 12-story building with 286 residential units and other student facilities, completed in 1993 on a slender lot immediately to McDonough's south. Like the library building, the Gewirz Center is traditional in style and very strong on urban design fundamentals -- it provides an emphatic, welcoming end point to the sequence of open spaces.

These efforts clearly set the stage for the addition atop McDonough's ample, empty platform. With its completion, Hartman-Cox now has Stone definitively surrounded; it has been, however, a gentle sort of takeover. The clash of styles, with Hartman-Cox's traditionalism playing against Stone's minimalism, is somewhat strained. But the new buildings are compatible with the original in materials and scale, and the outdoor spaces do much to pull the complex together. Stone's building remains as dumb and bland as it ever was, when you look closely. But because it no longer stands all alone in the sun on that stupid podium, you are no longer forced to look so closely.

The addition is a deft piece of work. The architects had less freedom here for the obvious reason that, unlike the previous buildings, this one is attached directly to the original. Or, to be precise, that point seemed obvious to Mario Boiardi, the Hartman-Cox partner chiefly responsible for the design of each of the new buildings. To another architect this condition might have seemed an opportunity to make a bolder, more contrasty statement. Boiardi, an experienced contextualist, preferred to respect Stone's building while, at the same time, delivering a pointed little critique.

Thus, the addition lines up with the original in height; it copies the flat protruding eave that is so prominent a part of Stone's design; as close as present-day brick manufacturing allows it matches in color and material; it even replicates the march of vertical piers and windows that makes Stone's design so boring. And yet, unlike the original, the addition has a hierarchical facade of base, middle and top; it is set back on the top floor to de-emphasize its size; it has a dramatic central entryway; though vertically proportioned, its windows are wider and more satisfying; its brick piers are fluted rather than flat . . . and on and on. All in all, it is a quiet comeuppance.

Hartman-Cox's architecture, here as elsewhere, is about deploying proven architectural conventions in fresh ways. It is an approach that works particularly well in historically sensitive locations, but gets chancier (or less necessary) in more open circumstances. The Georgetown Law site on downtown's edge, with vacant land all around and a deep freeway gash on one side, was a bit in between -- it definitely needed attention, but there was no strong context to suggest a particular architectural style. In this sense, Hartman-Cox's application there of a classical idiom was somewhat arbitrary.

However, it worked. The new buildings do indeed form a family. You can trace resemblances among them, variations on themes. Each, for instance, has a strong, semi-cylindrical entrance and, inside, striking circular rooms, yet no two are the same. Each building incorporates an arcade along its roof or porch, replicating a motif found in the open spaces. Each has one or more witty variations on classical fluting -- graceful ribs in a frieze, column or pier. Each has its own facade rhythms, its own decorative details, its own coloration and so on, but all within a basic system or beat.

It is an architectural fugue well played for the very joy of the playing, and to fix something that was broken (or at the very least functioning very poorly). As architecture, the Georgetown University Law Center still has its flaws, most of them dating back to 1971. But today it presents a more humane face to the world, and is a better place to work and study in. GEORGETOWN UNIVERSITY LAW CENTER Gewirz Student Center (completed 1993) Original McDonough Hall (opened 1971) Edward Bennett Williams Law Library (opened 1989) New addition (completed 1997) Exterior quad (completed 1989) CAPTION: Georgetown law school's McDonough Hall has grown to distinction thanks to architects Hartman-Cox. CAPTION: The brickwork on McDonough Hall's new section matches the old in color and material, but trumps it in warmth and architectural interest.