ON READING THE CONSTITUTION by Laurence H. Tribe and Michael C. Dorf (Harvard University Press: $18.95; 144 pp.). Constitutional theory has been in ferment for some years now, with lawyers and judges of every conceivable political allegiance--and some who claim to have no allegiance at all--arguing on behalf of what they consider to be the most appropriate reading of our most important legal document. In his latest book, written with a former student, preeminent legal scholar Laurence Tribe rejects all previous attempts to come up with a unified-field theory of legal analysis. Tribe and Dorf seem intent primarily on mulching the conservative theories of former Judge Robert Bork and sitting Justice Antonin Scalia before they take root, and do so easily; but they have little to offer in terms of a positive program, limiting themselves to asking "fruitful questions." But Tribe and Dorf's suggested emphasis on a case-by-case approach to law marks a retreat from theory, which, in this day and age, can only be to the good.