The Theatre-By-The-Sea, Matunuck, presents ``King of Hearts'' by Jean Kerr and Eleanor Brooke. Directed by Michael Murray; settings by William David Roberts. The cast:

Producer John Holmes has chosen a delightful comedy for his season's opener at Matunuck in Jean Kerr's ``King of Hearts.''

The dialogue is sharp, witty and candid -- typical ``don't eat the daisies'' material -- which has stamped the author throughout her books and plays, and it was obvious that the Theatre-by-the-Sea audience liked it.

The story is of a famous strip cartoonist, an arty individual, whose specialty is the American boy and who adopts a 10 -- year old to provide him with fresh idea material.

This is when his troubles begin, not to mention a fledgling artist who he hires, and who turns out to have ideas of his own, with particular respect to the hero's sweetheart secretary.

John Heffernan, playing Larry Larkin, the cartoonist, carries the show in marvelous fashion. His portrayal of an edgy head-in-the-clouds artist is virtually flawless.

This may be unfortunate, perhaps, from the standpoint of David Hedison, Providence's contribution to Hollywood, who is appearing by special arrangement with 20th Century-Fox. Not that Mr. Hedison does not make the most of his role. He does, and more. But the book is written around a somewhat dizzy cartoonist, and it has to be that way.

A word should be said for Gary Morgan, a Broadway youngsters who, as the adopted son, makes life miserable for nearly everybody and Larkin in particular. And for his playmate, Francis Coletta of West Warwick, who has a bit part, Billy.