UPDATE 1-Acea sees 65% dividend ratio over 2010-2012

* 2009 dividend will depend on tax arrears payment

* Plan will be updated when talks with GDF Suez conclude

* Acea shares close down 0.99 percent

(Adds more details, background, share price)

MILAN, Oct 26 (Reuters) - Italian regional utility Acea SpA (ACE.MI) aims to offer an average dividend payout of 65 percent of profits over the period of its 2010-2012 business plan, the company's chief financial officer said on Monday.

"For 2009 (dividends) we will have to wait and see the effect of the tax arrears decision," Giovanni Barberis told analysts in a conference call.

Following a government ruling on former tax breaks deemed to be in violation of EU rules as state aid, Acea has to pay tax arrears of 87 million euros. The arrears will be booked in Acea's third-quarter results, Barberis said.

"The presentation was a bit confusing. Their old dividend policy was for a 10 percent year-on-year growth. Now they are talking of an average of 65 percent on net profits we don't know...," a Milan analyst said.

"Also, I don't understand why they gave a new plan when they haven't decided what they're doing with GDF," the analyst added.

Acea and GDF Suez (GSZ.PA) have a joint venture in power generation in Italy and the French utility is eager to expand it to gas business.

"The talks (with GDF) are open. When this difficult work is concluded ... we will update the plan," Acea's chief executive, Marco Staderini, said in the conference call.

"We have to find the conditions to rebalance our relationship," he said.

Acea shares ended down 0.99 percent at 8.47 euros. The DJ Stoxx European utilities sector index .SX6P was down 0.29 percent. (Reporting by Stephen Jewkes; Editing by Greg Mahlich)