Crucial is perhaps too emphatic a word for Miss Sarton's short novel which lacks the urgency of the issue of her last one (As We Are Now, 1973) and deals with a common enough situation when Poppy, 50, decides to leave her husband, Reed, after 27 years of marriage in search of her ""Personhood."" This with only one token acknowledgement of Women's Lib. It is rather Watergate which has brought home to her the sullying business of compromise. Now Poppy, her children grown, is still a ""terribly unfinished, searching mass of conflict..."" and is determined to feel like an ""authentic human being"" and become a sculptor. Even if Reed had spent $20,000 on a studio for her, he had also given her constant migraines, colitis and ""despairs."" The conversations circumnavigate this ""life-enhancing"" decision and take place primarily between Poppy, Reed and Philip or Pip, friend of the family who has apparently held the marriage together longer than it should have been. That's about it -- a domestic sundry and no doubt Miss Sarton's readership, an unquestionably steadfast one, will not reproach her for what seems less than authentic (""dear heart,"" ""his secret treasure,"" etc., etc.) today -- almost protected from modern times.