The more impressive new movies fall into a similar pattern: beautifully textured and weakly dramatized. The latest exquisite invalid is Peter Weir's "Picnic at Hanging Rock," opening today at the Avalon 1.

An absorbing albeit inconclusive exercise in neo-Victorian Gothic contrived around the disappearance of a group of school-girls, "Picnic" has made a belated appearance in the United States. It opened in Australia in 1975 and proved a stunning critical and commercial success, perhaps the key work in confirming the emergence of a talented new generation of Australian filmmakers.

The film's attractions and drawbacks parallel those of Weir's own "The Last Wave," and also of "The Great Train Robbery" and "Agatha," which also attempt mystery melodrama and/or period evocation. A similar imbalance in style and content distinguishes current adventure melodramas like "The Warriors" and "The Deer Hunter." All these movies reflect the mixed esthetic results of attempting to finesse threadbare story material with alluring pictorial attributes.

The weaknesses in "Picnic at Hanging Rock" have been transposed faithfully by Weir and screenwriter Clive Bell from the original novel by Joan Lindsay. Although purportedly based on an authentic case, the premise of an unexplained mass disappearance is exploited for portentous, mysterioso effects that identify the storytellers as omniscient rather than merely speculative manipulators. The pretense of an unsolvable mystery is ultimately more perverse than justifiable. "Picnic" becomes a shaggy dog tale about persons "missing and presumed dead."

The fateful incident occurs on Valentine's Day, 1900. The students at Mrs. Appleyard's College for Young Ladies, a boarding school for adolescent daughters of the gentry located in the countryside northwest of Melbourne, set out upon an excursion that ends tragically. Following lunch in the woods at the base of Hanging Rock, a jagged, treacherous volcanic outcropping on the plains near Mt. Macedon three senior girls -- ethereal Miranda, piquant Irma and studious Marion -- vanish after climbing to the summit. A spinster mathematics teacher, Miss McCraw, also disappears without a trace.

Despite the expedient aspects of the disappearance, the filmmakers generate some dramatic interest in its aftermath by shifting attention to the emotional and social repercussions of the tragedy. For example, two concerned parties, the beleaguered Mrs. Appleyard (Rachel Roberts) and Miranda's adoring roommate Sara (Margaret Nelson), are eventually devastated by events caused by the disappearance.

An English youth, Michael, becomes so obsessed with the case that he makes a heroic attempt to search the rock after the official hunting party has given up. Aided by the coachman, a local boy named Albert with whom he strikes up an awkward friendship across class lines, Michael provokes the discovery of a survivor, Irma. However, this restoration of one of the missing girls is also turned into a gratuitously mystifying tease. After recovering from shock and exposure, Irma retains no memory of the illfated ascent of Hanging Rock.

In an equally gratuitous stroke of pathos, Albert and Sara are revealed to be separated orphan siblings. Poor Albert, very likably embodied by John Jarrot, who suggests what the Robert Mitchum character in "The Sundowners" might have been like as a young man, is even given a premonition of disaster right after we witness Sara sink into suicidal despondency.

Weir and cinematographer Russell Boyd exult in the Victorian furnishings and the erotic radiance of the girls in their flowing tresses and white muslin frocks as they glide through the formal confines of the school or the rugged, shadowy colonnades at the top of the rock. There are lovely fleeting images, like the sight of little boys running after the livery wagon as it passes through town, four schoolgirls primly perched on the seat facing the back.

Weir and Boyd succeed in giving the material at least a murmur of allegorical significance by contrasting the Victorian settings and attitudes with the wildness of the natural surroundings. Indeed, this contrast has begun to look like their specialty: an obsessive perception of how fragile civilized defenses may be against the forces of nature or the unknown.

At once emotionally sound and cinematically promising, this sort of obsession can degenerate into spooky nonsense unless it's handled with care. Weir's attraction to the mysterious seems authentic enough, but he's still not expert at rationalizing and sustaining psychological mystery stories. Both "Picnic at Hanging Rock" and "The Last Wave" lack consummate strokes of manipulative artistry. They leave you hanging on the brink, but the drop isn't very deep.