Ed Koch lends himself to caricature but no New York mayor seemed more like a cartoon character that Fiorello H. LaGuardia, the three-term charmer who read comic strips "to my kiddies" on radio during a newspaper strike.

This legendary example of LaGuardia's lese majesty attitude toward the dignity of his office is one of several wonderful scenes in "Hizzoner!," a new one-character Broadway show that opened last weekend at the Longacre Theater.The play was written by Paul Shyre as an expansion of his Emmy award-winning television docudrama and stars Tony Lo Bianco, who also played LaGuardia in the television version.

"Hizzoner!" is likable enough and good entertainment for most of the evening but it rarely digs beneath "The Little Flower's" epidermis to find the real man and what made him tick. Shyre has given us a caricature instead of a characterization and even as great a character actor as Lo Bianco cannot overcome the superficial material.

LaGuardia was depicted more sensitively as a complex personality in the 1959 Broadway musical "Fiorello!," which deals with LaGuardia's pre-City Hall years and his successful campaigns for Congress, where he served four terms. "Hizzoner!" serves to remind us that the time is ripe for the revival of that memorable Pulitzer Prize-winning Jerry Bock-Sheldon Harnick show.

"Fiorello!" had the advantage of a plot. "Hizzoner!" is merely a selection of old press clippings and excerpts from LaGuardia's writings and speeches presented more or less chronologically with an occasional flashback to establish LaGuardia's motivations.

It takes the form of the mayor's rambling reminiscenses voiced while packing up to leave his office at City Hall in 1945. A sculpture of a trylon and perisphere touches of anecdotes about the 1939 New York World's Fair. A baseball bat suggests a way to deal with drug pushers who were even then taking over the streets of the city.

There are some dubious passages in the play, especially the Italian-Jewish LaGuardia's mean-spirited imitation of Eleanor Roosevelt's aristocratic Knickerbocker intonations and the voicing of regret over having ousted Depression squatters in Riverside Park to build the West Side Highway.

This regret is shallowly rendered instead of dramatically demonstrating LaGuardia's overwhelming need for the moral approval of his public.

The retelling of LaGuardia's life emphasizes his eccentricities, prejudices, sentimentality, liberalism, street wisdom, and self-dramatization. But it shows us little of the master politician whose philosophy of progress meshed perfectly with those of President Franklin D. Roosevelt and city developer Robert Moses, the two men without whom LaGuardia might have been just another mayor, though more bombastic than most.

This is a diminished portrait of a man who yearned for greatness and nearly achieved it.

Lo Bianco never takes a breather and works up a plowman's sweat early in the show. He rants in a high-pitched voice, contorts his face with a variety of tics, lurches rather than walks, sweeps his arms like a windmill, points his finger, rolls his eyes and even reaches into the audience to bring a theatergoer on stage.

No cliche for impersonation is overlooked, which becomes tiresome long before the burned-out LaGuardia, warned by his doctor not to run for a fourth term as mayor, packs it in and fades away to await death, which came two years later. The play leaves us with a legacy of letdown instead of an inspirational bequest.

LaGuardia did have something pithy to say about fourth terms, however. He said they tend to make office holders "bossy." Lo Bianco looked right at Koch in the first night audience when he said it and Koch, seeking a fourth, seemed to enjoy the observation immensely. Will he heed the intended advice?

John Going has directed "Hizzoner!" so cleverly that Lo Bianco seems to fill the stage with people who aren't really there.

Eldon Elder effectively uses Federal architectural elements to suggest the mayor's office at City Hall, and the selection of memorabilia, including an exotic collection of hats picked up in LaGuardia's travels, is amusing.

Patrizia von Brandenstein had to design only one costume, a shapeless suit that speaks eloquently of LaGuardia's disdain for anything as frivolous as fashion.