Edit: "principal investigator" (english) matches "pesquisador chefe"(portuguese).
Be careful, in Portuguese there is a "investigador", but it's different from "pesquisador".
Pesquisador is researcher in the science, engineering, history and all sorts of academic fields.
Investigador is the one who goes after clues to find out something about somebody, or a criminal investigator.
I think Fonseman's translation sums up what you are describing: http://en.wikipedia.org/wiki/Principal_investigator.