Avant-garde encore.

The somewhat prosaically named Center for the Arts Theatre (CFA) at Yerba Buena Gardens in San Francisco is the main component in an ambitious urban grand plan begun over a quarter of a century ago by the city's Redevelopment Agency. The aim was to create a regenerative complex of buildings dedicated to the performing and visual arts on a 22 acre (9ha) light industrial site in the heart of San Francisco. The programme's cultural diversity is reflected in the architecture of individual buildings and over time this has thrown together some strange and slightly dislocated bedfellows -- for example Mario Botta's new San Francisco Museum of Modern Art jostles for attention in a Vitra-like tableau with Fumihiko Maki's low rise performance space and gallery.

Both Maki's building and James Stewart Polshek's new CFA Theatre are intended to be showcases for an exuberant and fluctuating array of local Bay Area performers and artists. This was to prove a key design determinant, but perhaps a more influential factor was the dearth of any obvious established physical context.

The freestanding 46 000 sq ft (4300[m.sup.2]) theatre occupies a flat, rectangular site and, unlike most buildings of its kind, all four elevations are clearly and permanently exposed. Historically, theatre designers have struggled with the typological challenge of large, windowless volumes. In the traditional urban theatre, impacted by adjacent context, the entrance facade usually became the principal focus, leaving the troublesome volumes containing the vast machinery of the stage and the acoustic chamber of the house safely buried out of immediate view. At Yerba Buena Gardens, the problem was compounded by the lack of an apparent main frontage with which to locate and signpost the building within the greater urban matrix. Yet Polshek's design courageously explores the latent possibilities of this unpromising situation, through a tectonic celebration of these predetermined volumes that succeeds in manipulating attention through a full 360 degrees.

The building's energetic, fractured composition was inspired by a need to create an intriguing yet comprehensible set of interacting forms that would delight both the theatre patron and casual passer-by. The primary relationship between the two principal volumes of auditorium and flytower, symbolically locked together by the proscenium, form a conceptual and physical basis for the design. The Yin/Yang interaction of the dark grey cube of the auditorium and stark silver trapezoid of the flytower is partly inspired by the traditional Japanese game of Go, played with small black and white pieces on a heavy, solid grid. Each additional component of the programme was defined as a distinct and identifiable form, assembled simply and logically in the manner of children's building blocks. These appendages modify, humanise and reduce the scale of the two main elements.

Prominent among the secondary volumes are the low-slung, white brick-clad support spaces (green room, loading docks and backstage) which wrap around the base of the flytower and a services tower that marks the position of the proscenium. This narrow, white-tiled wedge inserted between the main volumes effectively emphasises the critical, intersecting link between audience and performer. The entrance lobby is contained within a pristine glass cube which docks into the southeast corner and addresses Howard and Third streets. Projecting from this transparent volume, which glows lantern-like in the dusk, a Chinese red canopy imperiously signifies entry.

Connecting an essentially inward looking building with the wider drama of Yerba Buena gardens is one of Polshek's main preoccupations. Suspended above the canopy is a perforated metal screen, designed to receive slide or video projections from the roof of Maki's adjacent building. Eventually, visitors in the park, or in their cars, will be able to watch snatches of film drama on this giant video billboard. Similarly an external balcony slung along the west elevation is intended as an ad hoc performance space.

Inside, the subdued polarity of black and white gives way to visual vivacity. The lobby is dominated by a canary yellow wall and ersatz '50s streamlined detailing. A spindly industrial stair winds precariously up to the second floor lobby, providing a modest, modern promenade for Bay Area glitterati. The blurring of distinction between audience and actors on the theatre's exterior is also carried through to the inside. The 755-seat auditorium can merge with the stage, or the proscenium can remain intact and the building used as a traditional theatre. The spirit of informality and liveliness is reinforced by the walls of the auditorium, which are articulated by scaffold-like balconies that can be utilised as technical galleries in support of productions. The theatre's artistic focus is the challenging medium of the avant-garde, but the new building, with its sequence of abstract volumes and spaces, provides an equally stimulating encounter.