From Baltimore to Anchorage, "A Christmas Carol" is becoming to regional theaters what "Nutcracker" is to the ballet companies, a traditional holiday bill.

The New Playrights' Theater, now at L'Enfant Plaza's American Theater, has started what it hopes will become a tradition with confounder Harry M. Bagdasian as Dickens' latest adapter.

last night's opening for a series of morning, afternoon and evening performances through Dec. 29 amounted to a triumph of amiable grit over chilling facts. One can imagine Bagdasian saying to designer Russell Metheny: "Here's $6.27. See what you can do."

Accustomed to flexible intimacy,Metheny created portable flats which, with willing performaners inside them, can be turned into Dicken' many required scenes. Cut-out wood serves as props and 10 actors becomes 23 characters. In our labelminded age, call this one "The Poor Man's Christmas Carol."

Which is not, after all, fatal, for poverty was what Dickens set his Scrooge to alleviate. From the start, which had the players reaching the stage from the audience, the familiar story rose to its cheerful finale before an audience increasingly determined to get with its spirit. Bagdasian's contributions include imagined details which Joan Bellsey has staged in an hour's running time.

Ernest Joselovitz's "Splendid Rebels" will resume its 8 o'clock evening performances Dec. 27, to run through Dec 31. The L'Enfant Plaza Corp. virtually is donating its theater (nearly five times the 125 seats of the Church Street stage), and while the American is a far more formal place, last night's transition had a hospitable air in keeping with the season.