MEXICO CITY (Reuters) - Mexican President Andres Manuel Lopez Obrador on Monday slammed opposition lawmakers for voting down his planned constitutional overhaul of the electricity market, labeling it an act of "treason."

       Lopez Obrador has spent months championing the bill that would have tightened state control of Mexico's power market, but opposition lawmakers united on Sunday night to defeat the legislation that needed a two-thirds majority to pass.

       "I believe that yesterday was an act of treason against Mexico committed by a group of legislators who, instead of defending the interests of the people ... became outright defenders of foreign companies," Lopez Obrador said.

       Lopez Obrador's National Regeneration Movement (MORENA) and its allies fell nearly 60 votes short of the two-thirds total required in the lower house of Congress.

       Speaking at a regular news conference, the president struck a defiant tone, vowing "this is just the beginning," and urging lawmakers to get behind a separate bill he wants debated on Monday that will nationalize Mexico's lithium reserves.

       Under the lithium bill, Mexico would reserve the sole right to exploit the metal via a state-run company, and would not grant any concessions, the president said. Mexico does not currently have any commercial production of lithium.

       Lopez Obrador's proposed market changes would have done away with a requirement that state-run utility Comision Federal de Electricidad (CFE) sell the cheapest electricity first.

       Under the bill, the CFE would also have been set to generate a minimum of 54% of the country's total electricity.

       Earlier in April, Mexico's Supreme Court upheld key parts of a separate power bill from 2021 which the president argues will buttress his statist vision. However, a senator has challenged that decision, arguing that the court misread how justices voted.

       The court is due to debate other challenges to the 2021 bill on Monday.

       Lopez Obrador said he was not planning to put forward further energy initiatives during the rest of his presidency.

       However, he said he hoped whoever emerged as candidate from his political movement to succeed him in 2024 would again take up enacting a constitutional overhaul of the power market.

       (Reporting by Kylie Madry and Valentine Hilaire; Editing by Dave Graham and Hugh Lawson)