Child-Custody Cases Test Frontiers of Family Law
LEAD: Michele G. and Nancy S., a lesbian couple, had lived together for 11 years when they decided to rear children. Ms. G. found a sperm donor, took part in the artificial insemination of Ms. S. and was present in June 1980 at the delivery of a baby girl. On the child's birth certificate, Ms. S. was listed under ''mother,'' Ms.