* Analysts value BP's stake in TNK-BP at $25 bln
* AAR expected to place bid before Weds deadline
* Rosneft also likely to bid
By Melissa Akin
MOSCOW, Oct 15 (Reuters) - Bidding will open this week for BP's half of Russian oil company TNK-BP, with state oil major Rosneft tipped as the likely buyer of the British oil major's stake in the fraught but lucrative joint venture.
BP, whose chief executive Bob Dudley is due in Moscow on Monday for a meeting of foreign investors with Prime Minister Dmitry Medvedev, has booked $19 billion in dividends from its original investment of $7 billion in 2003.
It now stands to make a further $25 billion by selling its stake in TNK-BP, Russia's No.3 oil firm, after relations broke down with the billionaire quartet that owns the other half through their AAR consortium.
BP put its stake up for sale in June and the four tycoons - Mikhail Fridman, German Khan, Viktor Vekselberg and Len Blavatnik - are expected to bid by Wednesday, when BP becomes free to sell to a third party.
State oil company Rosneft could follow suit. Its powerful chief, Igor Sechin, an ally of President Vladimir Putin, told the Financial Times last week that the Kremlin chief had blessed the acquisition of BP's stake by Rosneft.
BP has said that it could also take a direct equity stake in Rosneft with some of the sale proceeds, which Sechin has described as a means of achieving government privatisation aims.
Analysts say a bid by AAR could amount to little more than a price pitch for a sale of its own stake in TNK-BP.
Both bids would be viable, say bankers, but it would require a clear signal from the Kremlin regarding the preferred outcome of the BP stake sale for financing to fall into place.
Rosneft has held talks with a dozen banks on raising as much as $15 billion in debt financing to back a cash and equity bid. AAR, meanwhile, is confident that it could fund its bid by leveraging up TNK-BP, which has low debts and huge cash flows.
AAR, which had been saying it wanted to buy BP's stake since the UK company announced its intent to sell in June, notified BP last week of its intent to sell its own stake, the first outward sign that Rosneft had a chance at getting all of TNK-BP.
AAR, bracing for rejection of its bid, is also considering a public offering of part of its TNK-BP stake. Rosneft is the only apparent buyer likely to mount a bid for its full stake.
"They are saying (to BP), you sell, and we'll tag along. They don't want to be left alone with Rosneft," said a source close to the BP-Rosneft negotiations.
The best outcome for Rosneft is, the source said, "to pay through the nose" and finance a buyout of both stakes in TNK-BP at a potential cost of $50 billion or more.
Even if bids are quickly made and accepted, the path to state ownership of TNK-BP may not be smooth.
Deputy Prime Minister Arkady Dvorkovich, a rival to Sechin for influence on energy policy and strong advocate of privatisation, has opposed Rosneft's bid, which would require government approval to go through.
TNK-BP management insists that the long-running conflict between BP and AAR has no impact, but the company has suffered a number of operational setbacks and management upheaval.
Sources close to TNK-BP said a decision to replace Alexander Dodds, a former ExxonMobil executive who quit his upstream post just a year after joining, with a former executive of Vekselberg's Renova group showed the oligarchs had tightened their grip on operations just ahead of the sale.