Former FTC Chairman Pertschuk here offers a rundown on five Capitol Hill campaigns won by ""public interest"" coalitions. Among the triumphs celebrated: passage of the Cigarette Labeling Act of 1984, which requires a rotating series of tough warnings on packaging and in print ads; defeat of an American Medical Association effort to exempt physicians from FTC regulation; renewal of a Voting Rights Act provision that will keep over a dozen states of the Old South under tight Federal supervision through 2007; and an interim victory putting a statutory cap of 50 on the number of MX missiles that can be built. The activist author provides blow-by-blow accounts of the political engagements, albeit mostly from the camps of the Davids--the Goliaths get short shrift or sneers and frequently both. Equally troublesome is Pertschuk's blind faith in the virtues of the liberal agenda. Too, since articulate, well-organized minorities have a knack for moving legislative mountains, it's often difficult to distinguish between special and public interests. Subtlety is not part of the author's canon, either. He unhesitatingly accepts public-interest lobbying as a selfless calling, both ""priestly and prophetic,"" and says the craft's successful practitioners release ""the unfocused energy of the public will."" All told, a tract only for those who know themselves qualified to determine precisely what constitutes a worthy, progressive cause.