Some people are born with it--like a good tenor voice or naturally curly hair--and those who have to work hard at becoming public speakers can only look upon such divinely favored beings with envy. Others assume that since it is only a matter of talking and they have been talking all their lives, they need no special preparation when they are called upon to speak in public. They frequently make fools of themselves.

Jack Valenti, the president of the Motion Picture Association of America and formerly a top aide to Lyndon Johnson, is probably one of the fortunate ones born with the knack. But he has worked hard at developing his natural skill and is certainly one of the most articulate, entertaining and persuasive public speakers of our time--even when he is speaking in a dubious cause, as the president of the MPAA must occasionally. He has also mingled with and carefully studied the techniques of other notable public speakers, and has distilled his experience and observations into a clear, simple set of rules that can be learned and put into practice by anyone who is able to form and enunciate a simple declarative sentence.

He admits right at the beginning that reading his book will not "make you one of the nation's great platform or television speakers." But he does supply the necessary guidelines that, pursued with a certain amount of diligence, can make almost anyone reasonably competent in this important and challenging discipline. The primary requirements are not literary genius or profound perceptions but a certain level of self-confidence, ordinary language skills and, above all, a capacity for hard work.

Many of Valenti's precepts are obvious: "Know what you are going to say." "Timing is the key to successful comedy." "A funny story should be practiced as diligently as an entire speech." "Anyone who appears on television would be well advised to try to watch a tape of that experience. You learn by what you see yourself doing." And so forth. But the simple fact is that most people who botch a public speech (and they are probably the majority of those who try this form of communication) do it by ignoring the obvious.

One of Valenti's instructions is less obvious and highly instructive, not only for the aspiring public speaker but for anyone who wonders how a book like this is put together.

"I keep a journal," he says, "and have done so for many years. Every time I find a line or two that I value in a book I underline it and later write it in my journal. Over the years I have accumulated a fat volume of over three hundred pages brimming over with words I have appreciated--stately lines from great authors, sprightly humor from antic wits. When I inscribe a quotation in my journal, I carefully note where I heard or read it, and from whom. If the item is from a book, I include the author, the title of the book from which it came, and the page number, so I can always refer back to the original to see the context in which it was said or written."

Clearly, his journal also includes personal experiences and observations as well as the gleanings of his reading because this book is full of them: The story of how Lyndon Johnson managed to mislead the media without lying through a careful choice of words, or the epic tale of a 45-minute speech in English delivered by President Ferdinand Marcos of the Philippines from memory, word for word as printed in a text that had been distributed to the audience.

We also have the complete texts of some admirably brief and effective speeches Valenti has given. One speech is given both in written text and the outline he made from it and used when the time came to speak. It is his speech on "The Changing American Presidency," delivered at the Cambridge Union in 1979 and worth studying for what it has to say as well as for the rhetorical techniques involved.

One may surmise that some of the material is included more because the author happens to like it than because it is absolutely essential to the book's message. And some is included because the essentials of what Valenti has to say could be compressed into 50 pages, but the publisher would have trouble charging $10.50 for a 50-page book.

In a sense, the book violates one of its own key precepts: "Edit. Prune. Extract everything you wish to emphasize and assemble those thoughts in your oral presentation. If you have a 50-page document you are presenting for the record, you ought to speak only some 10 pages." But that is partly because we like our speeches short and our books fairly long. Valenti's book is brief, pithy, useful--and when he digresses, he digresses through interesting material.