New York Times addicts know Warren Weaver as a knowledgeable analyst of Congress, once called the ""sapless branch"" by former Senator Joe Clark, a sentiment Weaver readily endorses. ""I have attempted to concentrate on the most flagrant inadequacies of the legislative branch,"" he writes. And the inventory is as formidable as it is familiar as it is frightening. Congress has relinquished its real authority to the executive, including its single most important function, financing the federal government. . . . Congress conducts its business under atavistic rules, ""facing nuclear problems with colonial procedures, insisting all the while that nothing is wrong,"" sinking evermore into sillybluster under the weight of the committee system, etc. . . . Congress is a dosed institution, usually self-protective of members' unethical and venal behavior. . . . Congress is ""a hall of illusions"". . . . Congress is crashing. Weaver also squirts some ink at his own profession -- congressional reporting is ""too homogenized,"" too bland, too collusive, too lacking in muscle to keep congressmen off their duffs. Finally there are specific recommendations such as TV coverage of deliberations, public financing of political candidates and development of an electronic information retrieval system. An informative, judicious, well written plague on both those deteriorating houses.