The party that Betty Comden and Adolph Green are throwing in the Kennedy Center Terrace Theater for the next two weeks is a family affair.

Comden and Green are like Aunt Betty and Uncle Adolph, the wildest and wittiest kin for miles around. You begin to think they're so good together that they should have gone into show business.

They did, of course. But Comden and Green became famous as writers, not performers. When they get up there and do their own stuff for you, they're still one step away from being complete professionals. Very occasionally, the pitch wavers or the joke falis flat. But who cares? It's all in the family, or so it seems.

The warmth and charm they radiate are elements that professionalism alone does not provide.

Green is irresistible. His white hair and sleepy eyes are a disgaise. Underneath his unprepossessing form is a manic man who can play an Andrews Sister and a macho goatherd with equal facility and enthusiasm. When he speaks a marble or two seems to be rolling around his mouth, but when he sings his baritone is loud and clear and his enunciation fiercely precise.

Comden is more frequently the straight person. Green surrounds her with frenetic activity and she responds with cool authority. When she does throw herself into more of the physical stuff, it's an exciting revelation: Aunt Betty has learned to boogie.

Their material includes songs they wrote with Leonard Bernstein, Jule Styne, Cy Coleman, Andre Previn, John Frank, Roger Edens and Saul Chaplin for shows and revues dating from 1939 to 1978. Some of it is very familiar ("New York, New York," "Just in Time," "Make Someone Happy," 'The Party's Over"), but most of it is not.

The most welcome discovery is a pair of songs from a 1951 revue, 'Two on the Aisle," written with Styne. Aunt Betty lets her aggravations at the man in her life really rip in "If," and "Catch Our Act at the Met" is a jolly comment on how showbiz can saturate the world of opera.

Their lyrics are quite clearly divided between the clever and the conventional. Clever is better, though sometimes it's not quite enough. Their lyrics seldom suggest much more than they say. Comden and Green spit it all out quite precisely, in both their clever and their conventional songs. A little more evocation might add some depth to their show.

"Some Other Time," a lovely song from "On the Town," comes close to suggesting a hidden texture. If Comden and Green would endow it with a bit more romance in the performance, it would be a knockout. But it's never forgotten that these two are just friends, not husband and wife.

They appear to be such wonderful friends, however, that it's hard not to join in the mutual admiration society. Just as at a family gathering, the audience claps when familiar showbiz totems ("Singin' in the Rain," Leonard Bernstein) are mentioned. And given the durability of Comden and Green as seen in this show, they deserve the bouquets with the best of them.

"You've made two old people very happy," they said just before whipping into "Drink to Me Only With Thine Eyes" set to the tune of "Stars and Stripes Forever" as an encore.

Of course it is they who have made hordes of American musical theater fans momentarily happy. Their party may be a bit heavy on the hors d'oeuvres, but practically everything is tasty. With hospitality like theirs, this party isn't going to be over for a long time.