* Center-right candidate Pinera ahead with 37 percent
* Still short of 50 percent needed to avoid run-off vote
* Despite split in left, no clear winner seen in run-off (Adds background, poll results for possible run-off vote, analyst quote)
By Rodrigo Martinez
SANTIAGO, Sept 3 (Reuters) - Chile's favored presidential candidate, billionaire Sebastian Pinera, held his lead over the ruling center-left coalition candidate Eduardo Frei ahead of December's vote, top pollster CEP said on Thursday.
CEP's survey showed that conservative Pinera would get 37 percent of the vote, unchanged from the last poll in June, while former President Frei saw his support drop 2 percentage points to 28 percent.
In a strong third-place showing was Marco Enriquez-Ominami, a left-leaning former film producer who pulled out of the ruling party, who gained 4 percentage points to 17 percent, the poll showed. The 36-year-old wants to boost the state's role in education and healthcare and raise royalties on mining companies.
Enriquez-Ominami's rising support mirrors deep divisions in the ruling "Concertacion" coalition that has seen some of its support fade after nearly 20 years in power.
Pinera, of the center-right National Renewal party, is the biggest electoral challenge to the coalition since it won office in 1990 after a 17-year military dictatorship.
Still, Pinera is short of the 50 percent needed to win outright without a run-off vote.
If the leading candidate fails to win more than half of the vote on the Dec. 13 election, he would have to face the second-place rival in a January run-off.
"Pinera did not meet his goal which was reaching 40 percent; that shows that his campaign has stagnated despite the problems of the coalition," said Ricardo Israel, a professor at Santiago-based Autonoma University. "Marco (Enriquez-Ominami) underscores the coalition's divisions, but he will not prevent a run-off between Pinera and Frei."
The CEP survey shows both Frei and Pinera closely matched in a second-round vote with 39 and 42 percent respectively. In the June poll, Pinera had a narrower lead with 41 percent of the vote against Frei with 39 percent.
Pinera, who owns stakes in a popular soccer team and a major airline, has lured voters with his message of political change to shake up what he calls n inefficient government.
His promises to boost the role of private business in the economy have put him at odds with powerful workers' unions, including those at state mining company Codelco, the world's biggest copper producer.
Frei, who was president from 1994 to 2000, has so far failed to benefit from the high approval ratings enjoyed by President Michelle Bachelet for her handling of the economy amid the crippling global financial crisis. He is expected to keep Bachelet's prudent economic policies, which have helped give Chile one of Latin America's most stable economies.
The CEP survey interviewed 1,505 people across the country from July 30 to Aug. 20 and has a margin of error of 3 percentage points. (Reporting by Rodrigo Martinez; Writing by Alonso Soto; Editing by Eric Walsh)