To look at the more heavily worked of Jake Berthot’s canvases, you’d never guess that his trademark rounded oblongs were fixed in geometric lattices complex enough to put Broadway Boogie Woogie to shame. But such works as the 1984 preparatory drawings for A Turning To, A Turning From lay out precise plans for the placement of the painter’s elongated, quasi-figural capsules. More striking still are Berthot’s tracing-paper overlay analyzing the armature of nested diamonds that shapes Cezanne’s Bather, and 1962’s Model and Mirror, in which the outline of a looking glass suggests what would become the painter’s signature form as surely as the rectangular railings of Mark Rothko’s 1938 Subway Scene foreshadowed the hovering fields of the older New Yorker’s mature work. Proportion is clearly as important to Berthot as it was to the abstract expressionist, but Berthot refuses to let planning constrict process. By the time Squaring Red (1993-94) was finished, little was left of its rigid structure; instead, the painting’s radiant, incarnadine swirlings are shot through by a single mustard-brown-outlined rectangle of blue and white, as if punctured by a bronzing shaft of sky. The Phillips is an ideal venue for this small show of the Berthot’s intimate abstractions and the studies that precede them. Not only are pictures by Mondrian, Cezanne, and Rothko close at hand, but the network of lines dominating 1994’s Study for Squaring Red suggests equally the architecture of celestial maps and the parquetry of the museum’s music-room floor. At the Phillips Collection, 1600 21st St. NW. (202) 387-2151. (Glenn Dixon)