Today, the nation's Press is more than the Fourth Estate; it is the Fourth Branch of Government. That's the provocative, eye-opening theme of Mr. Cater's wise, witty and exceedingly well-written book on the influence of the American press on government; and vice-versa. By stressing some issues and underplaying others, by timing, editing and outright suppressing, a reporter can startlingly affect the course of national events. As a striking example, Mr. Cater offers the Press' generous allocation of space to Sen. McCarthy, then the sudden ""dropping"" him after the famous Army hearings. Mr. Cater, the Washington Editor of the Reporter Magazine, writes cogently and persuasively of the Presidential press conference, ""leakages"" in government bureau operations, reporting from Moscow, the battle against too-tight secrecy controls, and other aspects of the Washington Press scene. This should be much-reviewed and much discussed. It also should be highly praised, for it is a valuable, one-of-a-kind examination of a modern American phenomenon. For university areas, urban areas, medium and large libraries.