Nonfiction briefly noted. . .; Paar's lemony postscript; P.S. Jack Paar, by Jack Paar. New York: Doubleday & Co. 360 pp. $14.95.

Readers who remember Paar's comedic talent on TV will expect his book to deliver fully on the promise of its subtitle: ''An Entertainment.'' True, among these jumbled personal anecdotes can be found many that are genuinely humorous. But some others are tasteless, vindictive, self-serving, or simply unfunny. I'm not saying you definitely won't like the book. I just advise you to take a long look before you buy.