(Repeats to remove sentences on links at the bottom of story)
* Gazprom Neft extends offer for mid-sized Sibir
* Indebted tycoon Chigirinsky, other large holders excluded
* Move by Gazprom Neft could boost output, refining
(Adds analyst comment, background on share issue)
By Melissa Akin and Olga Popova
MOSCOW, May 26 (Reuters) - The oil arm of Russian gas giant Gazprom agreed a takeover offer for mid-sized oil company Sibir Energy, Sibir said on Tuesday, in the state's first big play for the assets of indebted tycoons.
Gazprom Neft, Russia's fifth-largest oil producer, extended its 500 pence per share offer to all outstanding shares in the London-listed company, valuing it at 1.93 billion pounds ($3.07 billion).
The offer excluded its major shareholders -- indebted oil and real estate tycoon Shalva Chigirinsky, his partner Igor Kesayev and the City of Moscow.
Gazprom Neft gained a foothold in Sibir, a producer of 80,000 barrels per day of Siberian crude, in a bidding war with larger rival TNK-BP, paying a 70 pence premium to the rival offer for minority stakes and has since brought its stake to 27.5 percent.
A successful bid to consolidate Sibir, a partner of Royal Dutch Shell in a Siberian field, would boost crude oil output by 12 percent.
It would give Gazprom Neft control of the 200,000 barrels per day Moscow refinery, now shared with Sibir, and refining capacity would rise by 25 percent.
The expansionist oil arm of the world's largest gas producer has voiced ambitions to match ExxonMobil and BP in oil, and has made several small steps this year, acquiring Serbian refiner NIS and Italian assets from Chevron.
"My feeling is that Gazprom Neft is the most aggressive company in the oil industry right now," a source close to the deal said.
State-controlled Gazprom has dug deep into its pockets to make the offer, analysts said.
"The valuation was not that attractive, as according to our calculations, ABC + C2 Reserves are priced at $1.44 per barrel and refining capacity at $67.50 per barrel," UBS analyst Maria Radina said.
FOCUS ON SBERBANK
Sibir said in a statement that Gazprom Neft had proposed a cash offer for the entire company, excluding shares owned by Bennfield Limited, Central Fuel Co. and the Bank of Moscow.
Bennfield represents the holdings of Kesayev and Chigirinsky, with a stake of around 47 percent that is split between them.
The two men were forced to put up their stakes in Sibir as collateral with Russia's largest lender, state-run Sberbank, which helped them meet credit payments. Russian media have reported that Sberbank has been insisting on a change of ownership at Sibir.
The City of Moscow, which owns 18 percent of Sibir through Central Fuel Co has a political interest in stable fuel supplies from Sibir's stake in the Moscow refinery, owns 18 percent of Sibir through Central Fuel Co. It is seen as an unlikely seller.
Chigirinsky won a court order barring any transaction with his Sibir shares. Russian media have reported that Kesayev has agreed to sell his 23.3 percent to Gazprom Neft.
Sibir is suing Chigirinsky, who abandoned his plan to build Europe's largest skyscraper in Moscow when credit markets slammed shut, demanding he return $400 million advanced to him in a failed effort to sell his Russian property portfolio to Sibir.
Sibir, which said this week that Chigirinsky signed over 2.7 percent of the company, his Cote d'Azur villa and London mansion to cover part of the debt, said in its Tuesday statement that the Gazprom Neft offer would also cover any further share issues.
Banking sources said the company had left open the option of an additional share issue. New shares could be used to cover obligations on share options.
Sibir said it could not guarantee that Gazprom Neft would not seek its delisting if it acquired 75 percent of Sibir.
However, the source close to the deal said that Gazprom Neft was mopping up the last of the minority holdings in the company.
"They are effectively taking the company private," the source said. ($1=.6288 Pound) (Additional reporting by Dmitry Zhdannikov; editing by Jason Neely and Karen Foster)