* Center-right senator indicates he will back leftist Bachelet
* Senator opposed to HidroAysen dam, says Bachelet agrees
* Senator's support would let education reform pass
SANTIAGO, Nov 21 (Reuters) - The ambitious program of tax, education and electoral reforms that leftist Michelle Bachelet is planning for Chile advanced a step on Thursday after a senator from the right-wing coalition indicated he would likely support her.
Bachelet is almost certain to win the second round of Chile's presidential elections in December against Evelyn Matthei from the ruling right-wing bloc, but will need the backing of Congress to get her reforms through.
That backing looked to be on a knife edge after Sunday's elections, particularly in the senate. But Thursday's heavy hints from center-right senator Antonio Horvath that he would defect to her program could tip the balance in Bachelet's favor in the senate, in a blow to the ruling right.
The program Horvath wants "had convergence" with Bachelet's program, he told journalists as he left a meeting with her.
Horvath, a senator for the southern Aysen region, has campaigned hard against the planned local 2,750-megawatt hydropower project HidroAysen. He said on Thursday that he would back whoever would block the project.
HidroAysen, owned by Endesa Chile and Colbun , is expected to require around $8 billion in investment, including its transmission line.
Bachelet has called the project "not viable," but comments from Matthei's circle have been broadly in favor.
"There are some issues that are pretty clear," said Horvath. "We don't want a Patagonia with mega dam projects like HidroAysen. And she (Bachelet) agrees with that."
He said he would also talk to Matthei, but saw less grounds for agreement.
In Sunday's elections, Bachelet's bloc won 21 seats in the senate and 68 in the lower house - enough to hike taxes, but one short in each house for the higher majority she needs to push through wholesale planned changes to education.
In the lower house she is likely to get that support, with the presence of four left-leaning independent politicians, including two former leaders of a student movement that has been loudly calling for education reform.
Horvath's tentative support also takes Bachelet, who led the country from 2006-2010, closer to the majority she needs for electoral reform. She wants to change Chile's unusual electoral system, which effectively makes it tough for any party to win a sizeable majority in Congress.
To do that she needs the backing of 23 senators and 72 members of the lower house.
Horvath's comments are bad news for Chile's weakened conservative coalition, which gave up significant ground in Sunday's elections and is expected to lose heavily in December's presidential run-off.
Earlier on Thursday, current president Sebastian Pinera said he did not plan a comeback in the next elections in 2017.