"SHE SAW HERSELF perhaps as an Elizabeth Bowen heroine--for one did not openly identify oneself with Jane Austen's heroines"--so speaks Ianthe Broome, the heroine of An Unsuitable Attachment, Barbara Pym's "lost" seventh novel. For reasons unknown, her publisher rejected it in 1963 and a wounded Pym stopped writing. Rediscovered to critical acclaim years later, she wrote two last novels before her death in 1980. The never-published An Unsuitable Attachment was found among her papers and is now released here and in England for the first time. For Pym's admirers, a celebration with "a medium dry Spanish sherry" is in order.

They will not be disappointed. Filled with her trademark Anglican spinsters and bemused anthropologists, An Unsuitable Attachment is vintage Pym, the equal of Excellent Women, Less than Angels and A Glass of Blessings. The publisher must have been mad to reject this jewel. The cut-glass elegance of her precise, understated wit sparkles; her understanding of the human heart gleams more softly but just as bright. A writer with an extraordinary gift for the telling phrase, Pym uses humor tempered with charity. Perhaps because of her deep interest in religion, she never lampoons a character and, taken as a whole, her work reveals a tremendous compassion for lonely human beings.

Pym's quirky characters are the glory of her books and An Unsuitable Attachment presents a rich cast. Set in a run-down London parish, St. Basil's, it chronicles the adventures of various members of the congregation. The vicar is Mark Ainger who "although invariably kind and courteous . . . had the air of seeming not to be particularly interested in human beings--a somewhat doubtful quality in a parish priest, though it had its advantages." His wife, the cat-loving Sophia, behaves gracefully except when hunting down potential suitors for a younger sister, Penelope, a "Pre-Raphaelite beatnik," with a taste for tartan hot pants, false eyelashes and far too much purple eyeshadow. At 25, she has now "reached the age when one starts looking for a husband rather more systematically than one does at nineteen or even at twenty-one." Smitten with an older anthropologist, who unforgivably calls her "a jolly little thing," she stoutly carries on, aided by "a Mars bar she had happened to find conveniently to hand among the jumble of things on her bedside table."

The anthropologist cad is Rupert Stonebird, an archdeacon's son, who has returned to his childhood faith, and the attendant cups of tea in the rectory. Not the most romantic of men, he reflects midway through the book: "How convenient women were . . . the way they were always 'just going' to make coffee or tea or perhaps had just roasted a joint in the oven . . ."

He in turn covets the well-bred Ianthe, a mild-eyed canon's daughter, who exists utterly unconscious of her own charm. Tastefully attired in various "grey costumes," the thirtyish Ianthe works as a librarian, reads Tennyson and attends St. Basil's. Everyone sees her as "one of those splendid spinsters . . . who are pillars of the Church." Everyone, save John Challow, her unsuitable swain. Their romance, and the way it transforms Ianthe, are the stuff of this novel. In a surprisingly forthright manner, the usually reticent Pym deftly handles class and sexual differences and the barriers to love they often erect.

While An Unsuitable Attachment has its quota of overbearing grande dames and middle-aged bachelors still living with mum and chortling over misplaced semi- colons, it presents a moral lesson. Like Austen's Emma, it charts the growth of a single woman from ignorance to self-knowledge. Only after Ianthe has suffered can she be capable of love. John Challow is no Mr. Knightley, but he's quite wonderful nonetheless.

Stressing Pym's seriousness, though, denies the real pleasure of reading her. If one loves English eccentrics, who could resist a character like Daisy Pettigrew? Sister of a vet, she runs his cattery and "looked like an animal herself, moving sometimes like a slow marmalade cat, other times like a bustling sheep dog . . . She was sandy- haired and rather fat and usually wore blue or grey tweeds, though with the passage of years she had become comfortably indifferent to dress." If you have exhausted your supply of Jane Austen, An Unsuitable Attachment is thoroughly suitable summer reading.