IN "Love Over and Over," the title song of their new album, Kate and Anna McGarrigle sing "I'm goin' up a hill rolin' a boulder/tryin' to write rock and roll/but it doesn't keep body and soul together/So what do I know/or anyone know about love..." Of course, rock 'n' roll is the furthest thing from their beautifully crafted music, an entrancing synthesis of folk primitivism and pop pragmatism that is earnest but seldom solemn.

The McGarrigles, who perform at the Wax Museum tonight, have always been pop electics. With few exceptions, they base their sound on the old-fashioned acoustic graces of piano, accordion and guitar and the textured purity of their own voices. Like the instrumentation, the music is essentially timeless, comfortably rooted in folk melodies ("On My Way to Town"), Canadian chansons, traditional hymns ("Jesus Lifeline"), turn-of-the-century popular songs ("I Cried for Us") and Cajun dance tunes (a wonderful reworking of Bob Seger's "You'll Accompany Me," loosely translated into French).

Yet the McGarrigles modify these disparate influences with a thoroughly modern sensibility. On "Midnight Flight," Kate sings resignedly to an unidentified partner, "Now I'm not saying that I want to go/you're not saying that you want me to stay/and this moment doesn't come easy or often/so I'll take advantage and be on my way." Separation crops up in "I Cried for Us" ("Love, it's not I who didn't try hard enough..."), and elsewhere there's an edge of wariness and anticipation that shows that for all their roots in tradition, the McGarrigles have borne the weight of modern romance.

The love they know is not the hopelessly maudlin or overly caustic variety, but the kind that reflects the emotional, unbalanced roller coaster most people are familiar with. This works out well because each sister wields a distinctive pen: Anna tends toward innocent sentiment while Kate tends to be wary and defensive. The best example is the sisters' latest parenting song, "Sun, Son (Shining on the Water)," a soft-spun idyll about a child's dream/illusion on a long trip: "Big buildings at its center/stand ablaze with light/while lesser spires around these/entrap the beams in flight." The dream matter comes from Anna but the pragmatic kicker ("That's the sun, son, shining on the water") seems to derive from Kate.

Besides a clarity of vision, both Kate and Anna have another marvelous tool at their disposal -- crystalline voices that seem to come from a single, familiar heart; call it sibling harmony whose strikingly rich washes give weight to the solo lines at the center of each song. There is very little vocal embellishment but a barrelful of emotive confession.

In "Star Cab Co.," Anna evokes familial pride for a mother who has survived abandonment ("he's tied the knot again/with a younger and smaller wife," an acid line) and exhibited a resilience born of necessity. The rollicking "Love Over and Over," defined by the stinging guitar lines of Mark Knopfler, is a gleeful concession to pop energy.

"Love Over and Over" (Polydor 810-042-1 Y-1) is the McGarrigles' best album since their 1976 debut, "Kate and Anna McGarrigle," and 1978 follow-up, "Dancer With Bruised Knees." The supporting cast is mostly the same, the circle of friends who share the sisters' passion for spare acoustic energy, homespun wisdom and intense musical imagination. There are some weaknesses, including a tired reading of "The Work Song," but the McGarrigles have shown again why it's worth waiting for their infrequent albums and tours.

THE POWERFUL interplay of two women's voices is also at the heart of Trapezoid, a new-age string quarter hailing from nearby Elkins, W.Va. Lorraine Duisit and Freyda Epstein are not sisters, but there is a rare communality in the way their gem-like voices intertwine. Duisit, a pure soprano, is the ethereal pearl, and Epstein, a rustic alto, is the earthy ruby. Both shine on "Another Country" (Flying Fish FF287).

Trapezoid started out as a hammered dulcimer quartet, and the instrumental blend remains eclectic: Paul Reisler on hammered dulcimer and guitar; Ralph Gordon on cello and bass; Duisit on mandola, bowed psaltery and guitar; and Epstein on violin. However, since Duisit and Epstein arrived, the group's repertoire has become a swirl of traditional folk, swing and classical influences. The women add a sensual vocal dimension to a "folk-chamber music" concept that loosely ties Trapezoid to England's Pentangle.

"Another Country" starts off with a powerful retelling of the traditional lament, "Waggoner's Lad." The voices state the first verse in a cappella unison before dissolving into haunting harmonies riding over string embellishments. It's followed by the first of four Duisit originals, the mystic and melodious "Indian Paintbrush." Duisit pursues the sinewy Eastern melody in chilling counterpoint to the psaltery, a harp-like instrument played with a curved bow whose spare baroque sound is akin to the glass harp. The instrument also figures in Richard Farina's plaintive title tune and in one of three Duisit instrumental tracks "Kora," which most reflects Trape zoid's chamber-folk ideal.

The album is filled out by Epstein's a cappella version of Farina's "Quiet Joys of Brotherhood," Si Kahn's evocative and poignant "Sailing Alone" and a pair of swing-style jazz tunes. John Hendrick's lightly elegant and inspirational "Malice Towards None" (its melancholy air provokes some nifty interplay between voice and violin) is a winner, but the more up tempo and less convincing "Back in Your Own Backyard" sounds like watered-down Grappelli.

"Another Country" was recorded at Bias Studios in Springfield, and engineer Bill McElroy has done a marvelous job of drawing out the nuances in Epstein and Duisit's voices and the layered instrumental textures that make Trapezoid so intriguing. The McGarrigles and Trapezoid have both produced warm, intimate records that bear repeated listening.