DON FREEMAN took his editor's advice last year: that he create a sequel to CORDUROY, and bring back his overall-clad little teddy bear after a decade. A Pocket for Corduroy, published last week, turned out to be his final work.

His death on February 1 of a heart attack at 69 ended a productive career as creator of a gallery of anthropomorphic heroes - including Dandelion, Pet of the Met, Inspector Peckit, Norman the Doorman and Hattie the Backstage Bat - in a couple dozen affectionate, sensitive, often funny and occassionally moralistic children's stories.

What are th forces that inspire an artist to create - in one lifetime - backstage ping-pong players inElizabethan garb, riveters inside a bomber's nose and (in Penguins, Of All People! ) a sash-bedecked penguin envoy to the United Nations? What sparks a writer to describe a love affair with a city and (in Will's Quill ) the pastoral adventures of a goose who provides young Will Shakespeare with a fine quill to overcome a nagging case of writer's block? What emotions and compassions lurk in the background of a sketch of might-shift workers on a wartime assembly line, and between the lines of a story (The Seal and the Slick ) about a seal pup entrapped in a perilous offshore oil slick?

Some of the answers may be found in Come One, Come All (published in 1949), his memoir of the pre-World War II period; the backstage drawings that appeared in newspaper drama sections in the 1930s; the scenes of bomber plants and boot camps published in The New York Times Magazine in the early 1940s; three decades' output of children's books; and the recollections of friends and associates.

Cartoonist Al Hirschfeld was one of those friends. Together with William Saroyan (who wrote young trumpeter Freeman into one of his plays), scene designer Boris Aronson, theater critic John Beaufort, raconteur Alexander King and humorist S. J. Perelman, he was part of a scruffier, less formal version of the legendary Algonquin Round Table during the '30s. Freeman's self-published newspaper Newsstand , 30 or 40 pages of gossip, news and literature, was a staple of theatrical and literary circles in those days.

"He was 69 going on 30," Hirschfeld remarked a recent interview. "He always had the spirit of a young kid, a boyishness, a great love of life. There never was anything introverted about him.He was completely open."

Linda Zuckerman, the Viking editor who suggested the Corduroy sequel, recalls that he created, in his books and illustrations, "a childlike, spontaneous, unpretentious and apparently ingenuous world," yet actually prepared and paced his books meticulously. he never wrote down to kids, either. Designed for ages four to eight, his texts contained such words as raucous, reproving, solemnly, reluctant and inspired - to cite just a few.

His last book, regrettably, is not his best. Delicate, simply drawn in water colors and India ink, it carries Corduroy through a series of mishaps in a laundromat as he searches for material out of which a pocket can be made for his overalls. Typically unpretentious, it nonetheless lacks the bustling exuberance of Will's Quill , the high comedy of Dandelion or Penguins, Of All People! and the sensitivity of The Seal and the Slick .

Yet there may be another.

On a visit to Stonehenge last summer, the Freemans discovered that sparrow's nests had been there for years. A sixth sense impelled Freeman to begin sketching. The result - anunfinished manuscript of an adventure in flashback entitled The Sparrows of Stonehenge - arrived on his edit or's desk two weeks before his death.