With the exits of Noel Coward and Terence Rattigan, polite British comedy is in the deft hands of William Douglas Home, whose American imports have included "The Reluctant Debutante," "The Jockey Club Stakes" and "Lloyd George Knew My Father."

Now Rex Harrison, Claudette Colbert and George Rose star in Home's "The Kingfisher," which will get no closer on its way to New York than Baltimore's Mechanic Theater through Nov. 4. Those who pleasure in this genre, which implies more than witty lines immediately suggest will be rewarded.

Home's situation involves an amusing novelist who has learned of the death ("at the 17th hole") of the man who married the girl he had proposed to 50 years ago. Since she is to be in the neighborhood for her husband's burial, Cecil invites Evelyn "for tea" after the funeral, object matrimony. Cecil will propose under the tree where Evelyn turned him down in 1928. Complicating matters in New Hawkins, Cecil's testy, devoted manservant.

With but three roles, the players' chemistry is vital. Producer Elliot Martin proves an imaginative chemist in replacing the reluctant-to-travel London originals, Ralph Richardson, Celia Johnson and Alan Webb, who also benefited from Lindsay Anderson's invisible staging and designer Alan Tagg's highly visible tree.

Colbert is the miraculous element, looking, as she had in the National's 1974 "A Community of Two," exactly as she does in those stills from her 1934 Oscar-winner, "It Happened One Night." Upping printed records by a couple of years, Colbert boldly admits to being 75. That must be about right, for she made her Broadway bow 55 years ago. A lady of 50, who admits to looking a decade older than Colbert appears, remarked: "It's indecent."

Reclinging under Cecil's tree, able to rise without Hawkins' aid, the three soused septuagenarians bring down the house.

If you listen imaginatively, Home's lines define a delicately veiled liaison between servant and master. Rose's deft performance fills in more than meets eye or ear. This genre of polite comedy is by no means superficial. Sophistication is never sensational.