THE proportion of women in the world's parliaments has dropped from 15 percent to 11.3 percent in the past seven years. That nearly 25 percent shrinkage is reported in a new survey by the Inter-Parliamentary Union (IPU). The decline is ironic in view of the rise of women in the workplace, even in resistant cultures. The secretary-general of the IPU, which sponsored the survey of 106 nations with freely elected legislatures, offered one explanation for the drop. He noted that nations in the old Communist bloc often imposed quotas for representation of various segments of society in their rubber-stamp congresses. Another explanation, unsubstantiated, may be the ''Rosie the Riveter effect.'' Rosie was the generic name for hundreds of thousands of US women who went into industry and office jobs during World War II, only to be displaced when men were mustered out of the armed forces. An Israeli woman parliamentarian once told us that, during her nation's fight to exist, women served in many previously male jobs. But, as soon as the crisis period passed, they were expected to shift back into what she called ''more decorative roles.'' One answer to this societal reflex is to continue educating children to see leadership capability in individuals - not in some category label of man, woman, black, Hispanic, Asian, Christian, Jew, or Muslim. People select leaders according to ability within the mini-societies of their businesses, civic organizations, or churches. If they did the same on the broader canvas of national voting, we suspect the percentage of women legislators would be rising, not declining. And higher offices? Just remember the very effective Margaret Thatcher, Indira Gandhi, and Golda Meir. We rest our case.