There are a lot of famous families in pop music, but few are as extended as Kate McGarrigle's. The Quebec native and her sister Anna have made some of the best singer-songwriter albums of the past 22 years, often with an assist from their older sister, Jane. Kate's ex-husband is Loudon Wainwright III, an accomplished singer-songwriter in his own right, and their son, Rufus Wainwright, has released this year's best debut album, while their daughter, Martha Wainwright, is readying her debut. Anna's husband, Dane Lanken, is a longtime Montreal folkie, and their children, Lily and Sylvan Lanken, are up-and-coming singers themselves.

All nine family members take their turns at the microphone on the enchanting new album, "The McGarrigle Hour." So do Linda Ronstadt, Emmylou Harris and the McGarrigles' musical partner since childhood, Chaim Tannenbaum. Producer Joe Boyd and engineer John Wood, who worked on the first two Kate & Anna McGarrigle albums, are back in the control booth for this one. This is one of the rare reunion projects in which everyone seemed glad to see each other again, and the emotions of the event translated onto tape.

Kate & Anna revive a handful of their old songs, but there are also compositions from Loudon, Rufus, Martha and Tannenbaum. Harris joins the sisters on Jesse Winchester's "Skip Rope Song," and Ronstadt joins them on Stephen Foster's "Gentle Annie," which was mentioned in Kate's landmark composition, "The Work Song." The family's diverse influences are revealed in the Cajun two-step, the Bahamian hymn, the Sonny James honky-tonk number, the two old folk songs about Baltimore and the Cole Porter song in French. "The McGarrigle Hour," whose 21 songs take more than an hour, is a special album, every bit as remarkable as the family it documents. Appearing Monday at the Birchmere and Tuesday at the Ram's Head Tavern. To hear a free Sound Bite from the McGarrigles, call Post-Haste at 202/334-9000 and press 8132. (Prince William residents, call 690-4110.) CAPTION: "The McGarrigle Hour" features Kate and Anna, seven other kinfolk, Linda Ronstadt, Emmylou Harris and longtime partner Chaim Tannenbaum. ec