IN PETER Greenaway's 1987 "The Belly of an Architect," which starts a week-long run at the Biograph this weekend, Brian Dennehy plays a potbellied, American architect who has come to Rome to put on an exhibition in memory of the French architect, Etienne-Louis Boullee. So obsessed is Dennehy with this exhibition, not to mention himself, he doesn't realize his marriage with Chloe Webb is foundering and, like his father before him, he is dying of stomach cancer.

Of all Greenaway's works (including "The Cook, the Thief, His Wife & Her Lover" and "A Zed and Two Noughts"), this is probably the British filmmaker's least effective. As with all of his films, the choreography of people and objects before the camera (in collaboration with art director Luciana Vedovelli and cinematographer Sacha Vierney) is elaborate and splendid. The film also marks some of Greenaway's favorite thematic obsessions, including (in no particular order) spiritual and corporeal rotting, Sir Isaac Newton and arcane mullings on things historic, classical and numerical.

But Greenaway's narrative and his direction of actors -- two elements which only recently has he concerned himself with -- are without foundation. After the effects of the visual presentation have worn off, the film becomes rather tiresome to follow.

"H-2 WORKER," producer/director Stephanie Black's 70-minute documentary about ill-treated Cuban migrant workers in Florida, will screen at at 6 Sunday and 8:30 Monday at the American Film Institute. Black and Michael Hancock, the Farmworker Justice Fund executive director, are scheduled to attend both screenings and answer questions afterwards.

The AFI will also feature a Greta Garbo retrospective throughout July, starting this weekend with "Flesh and the Devil" (8 Sunday, 6:30 Monday); then continuing with "A Woman of Affairs" (6:30 Tuesday and next Friday), "Queen Christina" (double-billed with "Romance" at 8:30 Wednesday and Thursday), and "Two-Faced Woman" (6:30 Thursday). Call 785-4600 for the ongoing schedule.