With "The Forsyte Saga" and "Upstairs, Downstairs," public television proved that modern audiences, used to a diet of bare-bones drama, craved something richer. Now it is dishing up something really meaty, which is also served with the trimmings of costume and continuity that made those sagas so delectable.

"The Pallisers," a 22-part series that begins tonight at 9 and will be shown Mondays on WETA (Channel 26), is no mere dress-up soap opera. It is based on the six political novels of Anthony Trollope, a triumph of complex Victorian literature, in which the great themes of love and politics are seen with kaliedoscopic variety.

The books are a series only in that major characters in one apper as minor characters in another, and the family of the Dukes of Omnium are represented by three generations. Of necessity, the plots have been trimmed to give the television series a sense of orderly progression, and it has been skilfully done.

Lavishness and care characterize the production. The period has been reproduced magnificently, both visually and orally. It is not only Victorian clothes, interiors and manners that have been translated so they are convey quickly what a novel does at leisure, but also Victorian speech patterns.

The actors are dazzlingly right for their parts. Susan Hampshire as Lady Glencora, Barbar Murray as Madame Max Goesler, Roland Culver as the old Duke - these are only a few of the superb performances in large roles and small.

But all this makes it only the more heart-breaking that the hand that worked so hard and gave so freely - the writer was novelist Simon Raven - has been stingy with, of all things, human character.

With one or two exceptions, there are no true heroes or villains in Trollop - just contradictory human beings who are, in spite of their weaknesses, generally trying to do their best as they see it.

Raven has taken these people and restricted them to two motivations only - the desire for love and sex, and the desire for money and success. Duty is seen as a negative trait: Only those who aren't getting any of the goodies, anyway, because they are too old or frustrated or frigid, concern themselves with duty.

And yet perceiving what true duty was, and fitting it in with one's more personal objectives, was one of the chief preoccupations of Trollope's characters.

Consider the plight of Plantagenent Palliser, for whom this series is named. His is the classic dilemma of the property-owning liberal - a man filled with passionate beliefs which argue against his own interests. It was perhaps the height of liberalism for a Victorian husband to see his wife's desire to run off with another man from her point of view, and to feel he had no legitimate right to anger - but that is what he did.

In the novels, that is. For the purposes of television, he is an unsexy and therefore unobservant dullard, a stuffed shirt who muddles through because he has the big guns - the money, conventional morality, and the title - on his side.

Is it really so laughable, as it is treated here, that he was more fascinated by the idea of introducing decimal coinage into England than by teatime gossip?

Only sex and social climbing are treated seriously. And this involves some great twisting of Trollope's plots to explain why a sensible person might decide to pursue another goal.

Alice Vavasor, whose story constitutes the first Palliser novel, "Can Your Forgive Her?" is engaged to a quiet cultivated man whom she dearly loves. But because she wants to make a contribution to life, instead of merely enjoying the easy existence he represents, she decides instead to throw in her lot with her wild cousin who is seeking a political career. In this way, she is putting duty above love.

But the television show has reversed it. The explanation here is that the fiance is dull and the cousin is sexy, so naturally she prefers him.

A variation on that is the plight of Violet Effingham, who has been constantly refusing to marry a headstrong and violent man who is nevertheless faithfully in love with her. Trollope has her resist him for a long time, because of her realistic appraisal of his faults; and then to decide, also sensibly, that he is worthy and managable enough for her to be able to indulge in the luxury of taking him for a husband.

The television version? she is frigid until he kisses her with such force as to awaken her passion and put to sleep her reason.

Or consider Phineas Finn, the charming, weak, penniless Irishman who deliverately sets himself a course of falling in love with rich women and buttering up cabinet members.

Trollope has him spoil his youthful oppotunities - and find a sort of lowkeyed happiness - but not being able to stop himself from taking up Irish tenant rights and taking up with an Irish girl from his won type of background.

The television explanation? The girl is pregnant, and therefore he has to marry her. What else would compel anyone to do a thing so obviously against his selfish interests?

What else, indeed?