March 20 (Reuters) - Canada's main stock index fell at

open on Friday in broad sectoral declines and was on track for a

third straight weekly loss, as cautious investors monitored

developments in Middle East conflict, which is nearing its

fourth week.

At 09:31 a.m. ET, the Toronto Stock Exchange's S&P/TSX

composite index was down 0.4% at 31,731.87.