THE DEATH OF METHUSELAH AND OTHER STORIES; By Isaac Bashevis Singer; Farrar Straus Giroux; 244 pages; $17.95.

A sense of final reckoning is no stranger to the work of Isaac Bashevis Singer, but in this, his latest collection of tales, it's more pronounced than ever.The Nobel laureate allows readers to glimpse his intentions in a short preface commenting on the title story, which closes the book. Singer's unusual note is both illuminating and, one suspects, deliberately enigmatic. But it's evident that the author means "The Death of Methuselah" - which, significantly, he translated from his original rendering in Yiddish himself - to be a key to his own summing up in his 84th year of life.

Singer tells readers: "This story was not planned as most of my other work was. It almost wrote itself `automatically.' " He also relates that contemplating the confusion of modern man led him to consider humanity's corruption at the moment God was tempted to destroy all creation. Invoking the Old Testament and the Midrash, Singer defines that corruption as entirely sexual.

The author begins his title story with the matter-of-fact voice he has used often to lure readers into the mystical. "When you pass your 900th birthday, you are not what you used to be," he writes.

While Singer's work invariably recognizes the power of eros, and often observes the degrading effects of sexual obsession, he usually relates these episodes with wry tolerance. Still, his preface seems to invite readers to be skeptical of such neutrality.

Most of the tales sandwiched between the book's startling opener and end piece, are more or less modern. In several, Singer assumes his familiar pose of listening unjudgmentally to a story unfolded by a participant in it. As always, Singer shines as a storymaker. His focus is on character as revealed through his subjects' actions and brief musings. He economizes on description but nonetheless leaves readers picturing unfamiliar scenes - a shetel in the snow, a Yiddish newspaper office in Warsaw - while recognizing the universal foibles of men and women of distant worlds.

In the enduring spring of his imagination, but in the winter of his life, it seems that Isaac Bashevis Singer, has resolved to remind man of the consequences of letting go while reminding his God that human weakness is no accident.