Maverick leftist backs Chile's Frei for presidency

* Independent former candidate backs ruling bloc’s Frei

* Endorsement may help Frei’s bid, but impact seen limited

* Pinera tipped to narrowly win Sunday’s run-off

SANTIAGO, Jan 13 (Reuters) - Eduardo Frei, the candidate of Chile’s ruling center-left coalition, won the endorsement of a former independent candidate on Wednesday, which could raise his hopes of beating the conservative rival tipped to win Sunday’s presidential run-off.

Former film producer Marco Enriquez-Ominami had polled third in a December first round vote and missed the run-off, triggering a fierce battle between Frei and center-right billionaire Sebastian Pinera to woo his 20 percent support.

“Given the uncertainty that the right could block Chile’s march toward the future, it is my responsibility to contribute what I can so it doesn’t happen,” Enriquez-Ominami, the son of a leftist guerrilla leader slain during General Augusto Pinochet’s 1973-1990 dictatorship, told a news conference in parliament.

“So I formally declare my decision to support the people’s candidate who won 29 percent of the vote on December 13,” he said, referring to Frei, whom he had until now refused to endorse despite repeated appeals and concessions by the ruling coalition.

Sunday’s vote is expected to be very close, and a new poll on Wednesday showed Pinera having a slight edge over Frei, a former president. Analysts have said it may be too late for an Enriquez-Ominami endorsement to tilt the balance in Frei’s favor. [ID:nSAG002485] [ID:nN11148091]

Enriquez-Ominami said the right, now led by Pinera, was responsible for his father’s killing.

Pinera, who ranks No. 701 on the Forbes global rich list, won 44 percent in the December vote while Frei took 29.6 percent. It was the first time the right had won more votes than the left in a presidential vote since Chile returned to democracy in 1990.

A poll published by respected pollster MORI on Wednesday showed Pinera winning Sunday’s run-off with 50.9 percent of the vote, against 49.1 percent for Frei -- within the survey’s 3 percent margin of error.

Few expect any major change to prudent policies that have made World No.1 copper producer Chile a beacon of economic stability in the emerging world, whoever wins. [ID:nN11148468] (Writing by Simon Gardner; editing by Alonso Soto and Mohammad Zargham)