In ''Less Than Angels,'' published first in 1955 and now issued in America, anthropologists get the full treatment as Pym records their follies and pretensions with exasperated glee. Some bond of kinship, affection or self-interest ties the novel's characters to a research center in London. More a bemused observer than participant is Catherine, a hack writer, who stoically reflects, ''There are few of us who don't occasionally set a higher value on ourselves than Fate has done.'' Yet she delights in her busy, wayward solitude, relinquished from time to time when her young anthropologist lover, another fecklessly charming Tom, returns from the field. When an earnest young student from the suburbs falls for Catherine's Tom, relationships undergo uneasy realignments, while exotic new perspectives are opened, with bizarre backyard activities espied from upstairs windows. And throughout, whether in the leafy groves of outer London or the intellectual hotbed of the research center, where masterful women and evasive men grapple over grants, human couples of whatever sex demonstrate that there is generally one who must boss and one who must submit.