By Miguel Gutierrez and Adriana Barrera MEXICO CITY (Reuters) – Mexican lawmakers will send a landmark energy bill to Senate committees on Thursday to pave the way for debate on a cornerstone of President Enrique Pena Nieto's economic reform drive, a top ruling party lawmaker said on Wednesday. The bill, which would open Mexico's state-dominated energy sector to private investment in a bid to raise flagging oil output, will need approval of the Senate and lower house of Congress. Supporters say it is needed to raise slowing growth in Mexico, Latin America's second-largest economy. David Penchyna, leader of the Senate's energy committee and a member of Pena Nieto's Institutional Revolutionary Party (PRI), said the bill would be submitted to Senate committees on Thursday, but that the committees would not vote on it until Friday at the earliest.