Whether she's writing about a former trapeze artist saving her child from a burning home in ''The Leap'' or a violin that passes through generations of Ojibwe Native Americans in ''Shamengwa,'' Louise Erdrich can sketch a novel's worth of character and incident in just a few pages. Six tales in The Red Convertible are previously unpublished, but more than half the book is culled from her magnificent novels (five stories over 87 pages from Love Medicine, another five over 64 pages from The Beet Queen). The overall effect is less of a collection of ''selected and new'' stories than of a greatest-hits retread or a sneaky way to fill out a publishing contract. B

