Walt Disney's "Mary Poppins," first released in August of 1964 and revived in July of 1973, is back again.

This summer's reissue was a last-minute development, caused by the Disney studio's dissatisfaction with a new mystery thriller, "Watcher in the Woods." Its bookings have now been assumed by "Mary Poppins." In this case a headache for the studio should prove a treat for the public: "Mary Poppins" is durably enchanting.

And it is durable at the box-office: Last week it rose to tenth place on Variety's list of the 50 current top-grossing films in America, with reported receipts reaching over half a million dollars in one recent week alone.

The three big movie musicals of the mid-'60s -- "Mary Poppins," My Fair Lady" and "The Sound of Music" -- were linked by genre, popularity, chronology and Julie Andrews. Conspicuously present in both "Mary Poppins" and "The Sound of Music," she was conspicuously absent from "My Fair Lady." She had hoped to make her film debut recreating the role of Eliza Doolittle, but producer Jack Warner preferred Audrey Hepburn (not a disgraceful preference, of course, although it necessitated dubbing the songs), so Andrews agreed to make a belated starring debut with Walt Disney.

There was a happy ending -- for a while. Warner's production of "My Fair Lady" won eight Oscars in 1965, including best film of the previous year. Disney's "Mary Poppins" took five awards, including best actress for Julie Andrews. Her second film, "The Sound of Music," was already in soaring release the night she accepted the Academy Award.

"Mary Poppins" is one of the best things the studio ever did. Like all superior" children's movies," it's as likely to captivate adults as children, with a screenplay unusually tart and witty for a Disney production. The most appreciative kid's audience would be those old enough to identify with the juveniles in the story, who appear to be about 8 or 9. (The only drawback is that the film is a rather long 139 minutes.)

Disney evidently became interested in P. L. Travers' stories about efficient, eccentric Mary Poppins, the nanny with sometimes unsettling supernatural powers, in the late '40s, when one of his daughters began reading them. It was several years before he acquired the film rights, but once the project finally commenced, in 1960, the Disney studio did itself proud.

The Mary Poppins books are episodic, with each chapter a more or less self-contained adventure or anecdote. Screenwriters Bill Walsh and Don DaGradi adapted this material astutely: While maintaining a light, loose structure permitting frequent fanciful digressions and musical interludes they also provided a straightforward, coherent plot.

Mr. and Mrs. Banks (David Tomlinson and Glynis Johns) are portrayed as well-meaning but preoccupied and neglectful Edwardian parents. When Mary Poppins arrives, assuming supervision of the children, Jane and Michael (Karen Dotrice and Matthew Garber), after a number of nannies have resigned in frustration, she cheers up the household, quickens the imaginations of the children and awakens the parents to the needs of their offspring, who have been misbehaving in order to attract attention.

Neither father nor mother is expected to abandon preoccupatons (his banking career and her clandestine support of women's suffrage), but they are expected to pay more attention to the interesting children and put the house in order personally, instead of delegating domestic authority to the servants.

Parts of the film's appeal for kids may originate in this theme, which appears to express a young person's sort of reasonable expectation. Indeed, the movie seems to reflect a child's point of view rather more consistently than the books. Strict devotees of the Travers original may object to Julie Andrews as a softened, sweetened Mary Poppins. The truth is that she's a different kind of eccentric, the difference originating in the depiction of the movie nanny as a figure of wish fulfillment, a creature virtually dreamed into existence by the Banks children.

Mary Poppins can slide up banisters, clean rooms with a snap of her fingers, fly and sing like a bird. She has her strict, disapproving nanny side, but it's fairly restrained and never seriously prohibitive. In this context the prim, starchy aspects of Julie Andrews' personality have a faintly comic nature; they seem integral to the benign eccentricity of Mary Poppins. When she acts stern, one can't take her seriously, anymore than one can take the daisies perched in her hat seriously.

"Mary Poppins" is one of the few musicals created expressly for the screen during the early '60s, and it's considerably more imaginative than either "My Fair Lady" or "The Sound of Music," which were transposed from Broadway with inflated styles as well as inflated reputations. Looking back, it wouldn't have been such a bad idea if Hollywood had gone all out for "Mary Poppins" at the 1964 Academy Awards.

Two of the film's awards were unquestionably deserved: the Sherman brothers (Richard M. and Robert B.) for best original score and Peter Ellenshaw, Eustace Lycett, Robert A. Mattey and Hamilton Luske (The animation supervisor) for special visual effects. The Shermans also won an Oscar for best song, but their score is so pleasing that it seems arbitrary to single out one number -- in the case of the Academy, "Chim Chim Cher-ee."

I prefer the famous tongue-twister, "Supercalifragilisticeexpialidocious," and the lullaby "Feed the Birds (Tuppence a Bag)," which accompanies the extraordinary sequence of Jane Darwell as the Bird Women of St. Paul's Cathedral. This passage has a serene, haunting beauty seldom encountered in Disney productions. As a rule, the Disney artists seemed to specialize in comic or supernatural illusions, and the supernatural tendency often bordered on the nightmarish.

Almost all the illusions in "Mary Poppins" reflect a comic fancy: Merry-go-round horses fly off their moorings and run through an animated countryside; Ed Wynn as Mary Poppins' infectiously good-humored uncle hosts a tea party in midair. One is taken by surprise at the lyricism of the Bird Woman sequence and the moment when rain washes away the back-grounds during Mary and Bert's day in the country. These abstract effects are emotionally powerful; they lift the film from the charming to the stirring.

The most impressive sets are also abstractions: St. paul's, a few side streets, the rooftops of London during the elaborate, rousing dance number "Step in Time." While not as compelling as John Box's wonderfully evocative sets in "Olvier!," which imposed a moody, lopsided Victorian look, the "Poppins" backgrounds, graced by Ellenshaw's beautiful matte paintings of London vistas, are evocative enough. eThey transport us to an imaginative plane far beyond the conventional interiors of the Banks home and the conventional directing style of Robert Stevenson.

There are long stretches without Andrews, and a good deal of the time Dick Van Dyke carries "Mary Poppins" in the role of Bert, a versatile, ingratiating Cokney -- singing, dancing, clowing, playing a double role.

The vivid, amusing supporting cast includes not only Darwell and Wynn in brief, unforgettalbe appearances but also Reginald Owen as the dotty Admiral Boom, Elsa Lanchester as the outgoing nanny,Hermione Baddeley as Ellen the maid, Reta Shaw as Mrs. Brill the cook and Arthur Treacher as (surprise!) a police constable. Despite the distinguished old-timers, the best "old" character actor is probably Van Dyke in his impersonation of Mr. Banks' ancient employer.

"Mary Poppins," like "The Wizard of Oz," appears to be a film with limitless, timeless appeal for family audiences. The passage of time may even enhance its appeal. The deaths of Walt Disney and several of the older cast members have added a measure of poignance that didn't exist in 1964. In a less drastic melancholy way, so have the unfortunate turns in the movie careers of Julie Andrews and Dick Van Dyke during the 1970s.

Fifteen years ago "Mary Poppins" seemed like the Disney blockbuster in an era of musical blockbusters. Now it looks more precious: the least expensive but most inventive of the blockbusters; the last hurrah of Walt Disney himself; a classic of special historical interest and enduring, deepening popular appeal.