With that fabled Kennedy vigor, at 84 Grandma, as she likes to be called -- Belle Mere to her Francophile former daughter-in-law -- continues to dispense quantities of Boston cream pie, along with quizzes on math, languages and current events, to her 28 grandchildren; letters of instruction to her offspring (to her son the Senator, reminders of the correct usage of I and me); child-rearing advice to her daughters -- and to her readers, her strong beliefs in the virtues of thrift, discipline and religion. And one indulges her, not because she's entitled -- although undoubtedly that case will be made -- but because her earnestness is so downright appealing. One cringes with her at being called ""Dearie"" by a New York furrier (something that would never happen in Boston, she notes in an aside); smiles at her retort to her son after he gently admonished her to butt out of international politics (""Dear Jack: I'm so glad you warned me about contacting the heads of state, as I was just about to write to Castro.""); roots for her when she tries to bridge the generation gap with Bobby's scruffy teen-age daughter (""Can I give you a Dior dress? I don't know, Kathleen, what exactly do you like""?). It's impossible not to be moved by the poignancy of the joint London coming-out (the family was then at the Court of St. James) for retarded Rosemary and Kick (the second of her children to die, at 28 in 1948). And, yes, one cries with her, too, as Mrs. Kennedy walks the beach at Hyannis Port after the President's assassination, hour after hour asking why? why? why? But it's her husband who's most remembered here; he may have been no hero to his valet, but to his wife he was ""a superior person dedicated to goodness and efficiency."" Clearly the big book of the season -- and justly so. The lace-curtain Boston Irish princess, descendant only 100 years ago from ""muckers,"" has disported herself admirably. As Joe said the first time they called at Windsor: ""Rose, this is a helluva long way from East Boston.