What a refreshing discovery, in this dry season for commercially released movies, to come unsuspecting upon the vivid, original and engrossing films of the AFI's "New Indian Cinema" series, which begins tonight. Among the 11 features to be screened is a recent, wonderfully captivating picture by the country's most honored director, Satyajit Ray The rest of the sampling I made - pictures by younger, less well-known directors - bears witness to filmmaking talents of a very high order.

The endearing "The Golden Fortress," Ray's film, is the kind of movie you can't wait to see again. The plot - it's essentially a mystery story - is set in motion by a precocious 6-year-old boy, Mukul, who dreams of his life in a former reincarnation, amidst fabulous sights and wonders. As a movie with particular rewards for children, this one deserves to be set alongside such classics as "National Velvet" and "The Adventures of Robin Hood."

One of the defining attributes of such films is that age is no barrier to enjoyment, a rule which "The Golden Fortress" handily confirms. It's got everything we wish more of our movie fare had - a corking good story (written by Ray) full of action, danger and suspense; a minimum of violence; ample humor; striking visual composition and color photography; lively landscapes; excellent acting and a superb set of characters.

In a sense, the theme of the movie is that all men are children when it comes to adventure. Dr. Hazra, the parapsychologist who diagnoses Mukul's obsession, has the innocence of mellowed age; Bose and Barman, the laughably bumbling crooks who kidnap Mukul to track down the "golden fort" of his dreams, are like schoolroom scamps; the giddy Mr. Canguly, the mystery writer who tags along on the treasure hunt, isn't sure where life ends and make-believe begins; Felu, the resourcefuul detective who's out to rescue Mukul, is an intellectual who never left adolescence, and Tapesh, his teen-age assistant, plays Robin to his Batman.

There is a warmth to Ray's touch as a director that has very few parallels in Western cinema. Perhaps Jean Renoir, who was an inspiration to Ray's own career, comes closest, but Ray, in this picture at least, is even more open about his affection for his characters. It's contagious, too.

However deservingly, Ray's pictures have tended to overshadow the work of other Indian directors, especially in this country, where India films are seldom exhibited.That riches are being obscured is attested to by a film like "Two Faces: Indecision," written and directed by Mani Kaul. This is a rather more specialized movie than "The Golden Fortress" - more challenging and rarefied. But for anyone interested in the poetic possibilities of filmmaking, it may come as a revelation.

Based on a Rajasthani folk tale, it relates the story of a ghost who's so smitten with a young bride that he assumes the guise of her husband - who's away on business - makes love to her, fathers her child, and is eventually exorcised by the villagers, to the bride's great rue. The doubles - husband and ghost - are like two sides of the male nature, glory-seeking and romantic; and to the wife, they represent two often irreconcilable sides of her own being, duty and passion.

What's remarkable about "Two Faces" is the narrative method. There's no dialogue to speak of, and the only verbal intrusions are some introspective voice-over passages. Both the story and its emotional implications are set forth through a stream of lyrical images, with the help of some of the most sensitively used musical background I can ever recall encountering. The picture moves slowly, especially by Western standars, as do most Indian films. But once you've been snared by the Kaul's magic spell, nothing else seems to matter but the lovelorn ghost and his exquisitely brooding bride.

Time figures importantly in a third feature of considerable impact, Atwar Kaul's "27 Down," about an introspective young man, born in a railway car and destined to spend most of his life on trains.

A domineering father, lamed in an accident, forces him away from his artistic ambitions and into a career on the railroad. The rails lead him to love, too, but also transport him back to a graceless arranged marriage.

Photographed in sharply etched contrasts in black-and-white, the railway embiance - the rumbling cars, the chugging engines, the station platforms, the anonymous crowds, the chance encounters, the passing countryside - becomes a metaphor for all that is promising, romantic, transient, threatening and elusive about the hero's life. The film is somewhat somber in tone, but keenly sympathetic. The poignance of the story is intensified by the knowledge that the gifted young director drowned in a rescue attempt three weeks after completion of the movie.

The work of 10 independent directors over the past decade is surveyed in the AFI series, which runs through Sept. 29. Afterwards, the series will tour to New York, San Francisco, Minneapolis and Los Angeles.