Regulations of the FCC (Federal Clichés Commission) prohibit mention of Edward I. Koch in print unless accompanied by the world ''feisty.'' So let's get it over with quickly: Ed Koch was the feisty mayor of New York from 1978 through last year, when he was ushered out by voters. During his three terms he published three best-sellers. His new book carries the subtitle ''Letters from a Feisty Mayor,'' though much of it is the running (and score-settling) commentary of a feisty ex-mayor. Feist-lovers everywhere will want it for their collection.
But what about the rest of us? Those who live in less exciting, more habitable parts of the United States and have a tendency to gloat over other people's difficulties will always enjoy reading about New Yorik. Restive inmates of the city will find that the book revives the happy memory of long-forgotten complaints and provides some occasion for new ones. Readers inclined to literary criticism will note that the hero of All the Best a ''retiring, shy person'' who is transformed into a fearless Man of Brass who singlehandedly disperses a sinister cloud of gloom hovering over Gotham owes much to the superhero genre of comic-book fiction.
They also will note that the prose style derives about equally form the hard-boiled school of fiction and assault with a blunt instrument. Yet the prose and the book have a certain brazen integrity. If you disagree with him he provides ample opportunities you have to admit that Koch is bracingly plainspoken by the mealymouthed standards of current political discourse. And he has a positive genius for needling. After the Chinese government massacred students and other citizens in June 1989, Koch decided to name an intersection near the Chinese consulate in New York Tiananmen Square, provoking an indignant letter from the consul. In response, Koch invited the consul to defect and tell the truth, eliciting an even more indignant response, worthy of the haughtiest mandarin addressing the most impudent barbarian. But Koch has won the round, and he knows it.
Other targets include Donald Trump (''Trump's next book should be called The Art of the Steal''), an opponent of a homeless shelter named the Rev. Lawrence Lucas (''No room at the inn, Father?''), and numerous journalists Connie Chung, Joe Klein (''a bundle of neuroses''), Jack Newfield (''a politician with a press pass''), etc. Anyone concerned with our cultural heritage will be heartened to know that, in spite of their busy schedules and without so much as a single grant from the National Endwoment for the Arts, Mayor Koch and these devoted adversaries brought the art of insult and innuendo to a refinement hardly seen since the Italian Renaissance.
On the evidence of this book, Koch owed much of his vast initial popularity to his breezy impresonation of the smart, sassy city of the Jimmy Walker-Fiorello LaGuardia era, immortalized by the movies but othewise, as Koch found out, about as dead as a dodo. These days New York is permanently on edge, in a beleaguered, explosive, last-straw mood, and its cynicism is no longer cheerful. Yet for a time, Koch cheering on commuters trekking across the bridges during the transit strike of 1980, insulting foreign dictators, saving some wild roosters in Staten Island brought an antibureaucratic rashness to city hall and raised the city's morale. The trouble was that some of the rashness also hurried it along to a state of siege. It might have been better for the city and for this book if Koch had reverted a few years ago to that elusive ''retiring, shy'' alter ego, who could have done a milder, more reflective commentary on these often compleeing, often grating letters. B