"CAN'T FIGHT," says the dragon, "won't fight! Anyway, why must I be defeated?" "Because it's in the story," says St. George.

Actually, they don't say it; they sing it. And they are not really St. George and the dragon; they are Anthony Holt and Bill Ives of the King's Singers, guest artists with the National Symphony Orchestra for this week's Christmas-oriented pops program in the Kennedy Center Concert Hall. In its varied bundle of Christmas music, the British group is including "The Reluctant Dragon," a mini-opera (without scenery or costumes) based on Kenneth Grahame's book of the same name.

Composer John Rutter has tailored the music specially for the King's Singers' style, which ranges from madrigals to be-bop, and has also thrown in brief parodies of Benjamin Britten and British patriotic music in general.

As performed on one of the King's Singers' recent records, "The Reluctant Dragon" is a tiny comic masterpiece, and the interpretation upholds the group's reputation as one of the world's finest and most versatile musical organizations. The record (which also contains Rutter's treatment of another Grahame book, "Wind in the Willows") is so far available only as an import from England, but a limited number of copies will be on sale at the performance or at Olsson's Books and Records. Other King's Singers albums (in a discography that spans dozens of titles) are widely available in Washington record stores.