It would be comforting to believe the rumor that "Love on the Run," opening today at the K-B Janus and Cerberus, will be the last installment in Francois Truffaut's doddering series of films built around the semi-autobiographical character Antoine Doinel. However, the "series" looked overdue for cancellation when "Bed and Board," an insipid chronicle of Doinel as an oblivious young husband, appeared in 1971.

After swearing off for eight years Truffaut has revived the poor wretch with even less freshness. Indeed, "Love on the Run" is such a self-derivative triviality that a substantial percentage of the running time is devoted to excerpts from the previous Doinel films.

Truffaust must fall back on Doinel whenever he has nothing more urgent or original in mind. It's possible that the character allows him to work off a few guilt feelings about his own romantic vicissitudes or unresolved longings. The women in "Love on the Run" scold Doinel for his incorrigible emotional immaturity, and Truffaut interjects a lengthy maudlin interlude in memory of Doinel's neglectful mother, who has died and been buried next to Marguerite Gauthier, of all heroines, in Montmarte.

In "Love on the Run" we're suddenly confronted with the myth of Madame Doinel as a saintly paramour, the soulmate of the Lady of the Camellias herself. There's no justification for such canonization on the evidence in "The 400 Blows," the first movie about Doinel. Presumably, Truffaut is indulging a belated wish to forgive his parents publicly for their well-publiczed neglect.

"The 400 Blows," Truffaut's first feature, remains the only essential Doinel movie. Jean-Pierre Leaud seemed an extraordinary embodiment of a troubled but basically resourceful kid when he played Doinel in "The 400 Blows," at the age of 14. He was steadily diminished in the role in the course of 20 years. In a curious reversal of expectations his Doinel has "grown" to look less intelligent, less appealing and less capable with every new encore.

Leaud's decaying youthful image is exaggerated by the attractiveness of the actresses who surround him. Marie-France Pisier, who played a girl Doinel was infatuated with in Chapter Two-the "antoine and Colette" episode of the anthology "Love at Twenty"-turns up in "Love on the run" looking better than she did 16 years ago. Claude Jade, who made a charming debut in "Stolen Kisses" and returned as Doinel's young wife Christine in "Bed and Board," revives the role in "Love on the Run." Like Pisier, she seems to improve with age.

In addition, Doinel has acquired a cute, lively girlfriend named Sabine, played by an actress known as Dorothee, as consolation for the loss of Christine, who divorces him amicably in the first reel. Between the extended passages of excerpts Truffaut throws in a few newly invented recollections. One involves Doinel in a brief affair with Christine's best friend Lilliane, played by an intriguing new actress called Dani, after the dear boy has tormented himself into a dirty-minded slow burn imagining hanky-panky between the girls.

The Doinel movies have always lacked the serial integrity and appeal of the Thin Man mysteries or James Bond adventures or even the nominally self-contained films of comic stars like the Marx Brothers, W.C. Fields, Bob Hope, Red Skelton and Woody Allen. "The 400 Blows," which grew out of an urgent autobiographical impulse, was self-contained, and it can stand on its own. The subsequent films have been superfluous. "Antoine and Colette" was merely a sketch, "Stolen Kisses" a pleasant trifle.

In "Bed and Board" and "Love on the Run" Truffaut's once autobiographical protagonist has continued to shrivel into twerphood in a setting of inane romantic comedy.