The promise that flickered unevenly through Alain Tanner's second feature, "La Salamandre," released in 1972, has now matured into an illuminating and affecting style of lyric social comedy and character delineation in his fifth feature, "Jonah Who Will Be 25 in the Year 2000," opening today at the Dupont Circle.

Tanner's singular, exhilarating triumph has been to create a politically and socially conscious movie that keeps a humorous, affectionate glow on.

His view of the ongoing, bittersweet comedy of existence, where hope springs obstinately eternal amid deferred, derailed, rerouted or exploded hopes, may seem all the more persuasive for being expressed so casually and playfully. Without any apparent effort to sound profound or impose a viewpoint on the audience.

Tanner, a Swiss who resides in Geneva - the setting of "Jonah" - and works in French, seems to have enlarged his range and vision while streamlining his techniques. "La Salamadre" was a fitfully beguiling composition for a trio of spiritual eccentrics and non-conformists.

"Jonah" is at once more expansive, lucid and satisfying. The trio has grown into an octet, augmented by a significant ninth character a generation older than the basic group and a 10th presence a generation younger the title character, who is born in the course of the story and acquires a symbolic importance far beyond his years or brief appearances on the screen.

The eight principal characters, whom Tanner has described as "minor prophets," may be subdivided into four couples, two married and two in the process of forming romantic attachments which may or may not continue.

The names of these characters begin with the letters "Ma": Max, Madeleine, Mathieu, Marcel, Marguertie, Mathilde, Marco and Marie. Nothing is made of this "concidence" in the movie itself, but the "Ma" group has certain nurturing, hatching, creative instincts in common.

Their "Ma" - ness is expressed in a variety of urges, plans, hobbies, professions or life styles. It's a literal maternal instint in the case of Myriam Boyer's pretty, plump, patient Mathilde, who professes to abhor empty spaces. He husband Mathieu (Rufus), a printer and union leader laid off during a recession, secures a job at a small farm owned by the other "Ma" married couple, Marcel and Marguerite (Roger Jendly and Dominque Labourier). Thwarted in his hopes of teaching an experimental school on the farm. Mathieu takes a factory job and vows to sustain his ideals while plugging away to support Mathilde and their four children, including their freshest hope and creation, the newborn Jonah.

Marguerite's energies are concentrated on growing organic vegetables. Tough and brusque, she is determined to avoid chemical additives and fertilizers, even though she acknowledges that the organic approach is more arduous and less productive.

Solitary, scruffy Marcel is absorbed in his avocation of photographing and sketching animals. "People have no mystery." he tells Mathieu during their first encounter. Jacques Denis' personable Mario is a neighbor of Marcel and Marguerite. He occasionally borrows produce to illustrate his history lectures in high school. Typically, Mario begins his course of instruction by removing a cutting board, a butcher knife, a metronome and a coil of blood sausage from his brief-case, preparatory to riveting his startled, delight students with his concepts of time.

Mario will eventually abandon high schools for old people's homes. Perceiving the present and future as "the revenge exacted by the past," he becomes convinced that comforting the old is a more urgent need than preparing the young.

Mario is attracted to a young woman already specializing in charitable deeds on behalf of the elderly Miou-Miou's Marie is a French girl employed as a cashier in a Geneva supermarket. She relieves the monotony of her job - and the contempt she feels for it - by undercharging certain customers, mainly the elderly. She also supplies a neighbor, a retired railroad employee name Charles (Raymond Bussiers), with cut-rate groceries.

Jean-Luc Bideau's Max is a disillusioned former activist, a journalist who participated in the agitation that led to the downfall of DeGaulle in 1968. Now employed as a proofreader, Max has become hooked on roulette. He encounters Myriam Meziere's Madeleine, a secretary who believes in the universal efficacy of eroticism in accord with Tantric rituals, in the company of a piggish old school acquaintance who has since become a bank officer. Learning of a pending land speculation scheme, Max decides to alert the potential patsies, who include Marcel and Marguerite. Madeleine agrees to help by passing him copies of bank documents that verify his suspicions of dirty business.

Tanner maintains an extraordinary balance between sysmpathetic and critical observation. One is drawn to this obscure, divergent group of radicals, utopians, rebels and dreamers without losing sight of the flawed or incorigiable aspects of their particular characters and survival techniques. Tanner realizes how one form of radical or utopian can grate on another. Marguerite's animostiy forces Mathieu to abandon his fledgling school. Moreover, her hostiltiy is justified to a considerable extent. Max looks upon the pursuits of the other "Ma" characters with frank disdain. The opportunity for the only kind of change he recognizes, a change of political systems, has been lost. He considers the other character's hopes merely fads and delusions.

While Tanner would probably share Max's criticisms of the existing system, he evidently rejects the idea that politics is the only means of social change. The setback that has virtually immobilized Max the activist seems to have convinced Tanner of the creative or possibly therapeutic value of other approaches. Even if theyseem like futile or crackpot approaches, they may sustain hope and nurture change over the long run.

Ultimately, Tanner seems to derive inspiration from the sheer human diversity, vitality and eccentricity of the characters. He doesn't dissociate ideas from human beings: on the contrary, they animate each other.

Tanner, who is now 47, claims to have been profoundly influenced by the political upheavals of '68, but the lasting influence may have been more emotional than political. He seems genuinely fascinated by the variety of ways in which people act, think and try to cope with their situations in life. This democratic, inclusive impulse seems to keep his social analysis well lubricated. The arguments don't get dry because the people expressing them are to vivid and varied. Tanner believes in the unconscious, in hidden, untapped possibilities. Marcel's remark that people have no mystery represents the exact opposite of Tanner's attitude.

Tanner and his photographer, Renato Berta, have evolved a remarkably fluid, attentive, unobtrusive camera style.

During one marvelous sequence Berta's camera inscribes a circle, moving clockwise around the dinner table as the "Ma" group suggests names for the child Mathilde is expecting, settles on Jonah and improvises a little song that also provides the movie with its title. The circuit begins and ends at the empty place at the place, emphaszing the absence of Marie, whose larcenous generosity has landed her in jail.

Tanner doesn't fail to notice the mocking empty spaces even while expressing his characters' warmest moment of community. It's the finest single example of the complex, humane vision that informs his comic dubious, possibilities of human nature.