Sometimes Francesco Cavalli's opera "La Calisto" is like raunchy Gilbert and Sullivan. Sometimes it sounds like the stately music dramas of Monteverdi. Its plot is a running battle between the sublime and the (intentionally) ridiculous. Both are well represented in the production that opened last night and will close tonight at the Wolf Trap Barns. Most of the time, the ridiculous seems to be winning, but the ending is sublime and it works.

With a plot too kinkily complicated and a cast of characters too large to discuss in detail, "La Calisto" is essentially a drama of cosmic miscegenation. Its characters include gods, goddesses, mortals and a rich array of nymphs, satyrs and furies. All possible sexual combinations are tried, or at least suggested, except one human being with another.

Jove, a celestial philanderer who finds eternity too long for monogamous fidelity, falls in love with Calisto, a huntress who has taken a vow of celibacy. Chaste makes waste, thinks Jove, and he disguises himself as Diana, the virgin goddess of hunting whom Calisto worships not wisely but too well. The maiden who resisted his virile advances eagerly accepts his maidenly embraces. Meanwhile, Diana finds her own chastity challenged by the goat-god Pan and his faithful cortege of satyrs as well as the moonstruck shepherd boy Endymion. Plot complications include the abduction and almost the murder of Endymion by the satyrs, the terrible wrath of the statuesque Juno, who thinks eternal monogamy is a good idea, and mistaken identity when Calisto asks the real Diana for more of the divine cuddling she had from the false Diana.

The climax of the opera's sublime segment--probably the element that sold the most tickets in 1651 when it was new--comes with the double metamorphosis of Calisto. First, Juno turns her into a bear--an eminently huggable bear as portrayed by soprano Nicole Philibosian--then Jove transforms her into a whole cluster of heavenly bodies. He doesn't make her a star; he makes her a whole constellation.

Musically, the opera begins rather slowly and has (for modern tastes) perhaps an excess of languishing in the love-smitten roles of Calisto and Endymion. But comic relief is abundant and by contrast makes the serious parts more effective. By far the most spectacular comic talent in this production is tenor Colenton Freeman, who plays--improbably but with tremendous flair--the role of Linfea, an aging nymph who wants a husband but draws the line at satyrs with the funniest line in the show: "I don't make love to nanny goats." The rejected satyr is deliciously portrayed by a soprano, Dale Wendel. Four other satyrs (male) constitute a superb quartet-chorus.

Perhaps the most virtuoso performance of the show is that of mezzo Meredith Parsons, who plays both Diana and Zeus-as-Diana and manages to make it always clear, by gestures, posture and tonal quality, who she is at any given moment. Other distinguished performances in a generally fine cast are given by Katherine Henjum as Juno, Peter Atherton as Jove and Kurt Link as Pan. Lee Velta as Endymion has an excellent baritone voice but it was not always completely secure in Act I. David Hamilton sang the role of Mercury well but did not have the stage presence of the fleet-footed messenger of the gods. Hal France conducted a well-paced performance that was clearly aware of early baroque style and conventions even when it bent them a bit to modern tastes.