UPDATE 2-Entergy unit to buy Louisiana natgas-fired plant

* Entergy to begin purchasing plant's output in May 2010

* Sees 2010 operational EPS $6.40 to $7.20

* Entergy board authorizes $750 mln stock repurchase (Updates with 2010 forecasts, share repurchase)

HOUSTON, Oct 30 (Reuters) - Entergy Corp's (ETR.N) largest Louisiana utility said it has agreed to acquire the 580-megawatt Acadia 2 natural gas-fired unit near Eunice, Louisiana, from independent Acadia Power Partners LLP.

The combined-cycle unit, completed in 2002, becomes one of the most efficient gas-fired units in Entergy Louisiana's fleet and will help lower the utility's fuel costs, Entergy said in a release.

No financial terms were disclosed.

Entergy Louisiana will purchase all of the plant's output beginning in May 2010. The acquisition is subject to regulatory approval and is not expected to close until late 2010 or early 2011.

Under Entergy's system agreement with its utility affiliates, it will sell one-third of the Acadia output to Entergy Gulf States.

The two-unit Acadia plant, totaling 1,160-MW, was built as a joint venture by a unit of Cleco Inc (CNL.N) and Calpine Corp (CPN.N) which later filed for bankruptcy and sold its interest to a third party for $189 million.

Earlier this year, Cleco Power LLC purchased 50 percent of the Acadia plant for about $300 million.

Pineville, Louisiana-based Cleco will operate both Acadia units, according to the Entergy release.

Separately, Entergy said its board had authorized an additional $750 million repurchase program.

Entergy said on Friday it estimated 2010 operational earnings per share would be in the range of $6.40 to $7.20. It also said it anticipates capital expenditures of $7.1 billion between 2010 and 2012.

New Orleans-based Entergy, owns and operates about 30,000 MW of generating capacity, markets energy commodities, and transmits and distributes power to 2.7 million customers in Arkansas, Louisiana, Mississippi and Texas. (Reporting by Eileen O'Grady; Additional reporting by Phil Wahba in New York; Editing by Marguerita Choy, Gary Hill)