* Bulgarian Q3 GDP up 6.8 percent, vs snap estimate of 5.6 percent.
* Romanian Q3 consumption jumps 13.7 percent, vs 9 percent Q3 2007
* IMF slashes Bulgarian 2009 GDP forecast to 2 percent, says Bulgaria has not asked for aid.
* Romanian coalition official says Bucharest may be forced to ask IMF for 10 bln euro credit line
* Austrian cbank warns capital flow into eastern Europe could halt if lenders face trouble.
(Adds IMF forecast on Bulgarian 2009 GDP)
By Tsvetelia Ilieva
SOFIA, Dec 15 (Reuters) - Consumer demand in Romania and Bulgaria surged in the third quarter, fuelling growth, but economists said it was already losing steam due to the global crisis and the EU newcomers faced a steep drop off next year.
The IMF slashed its 2009 forecast for Bulgarian growth and Austria's central bank, which oversees some of eastern Europe's biggest investing groups, said the capital flow into the region could halt if western lenders faced refinancing problems.
Following decades of sluggish development and austerity since the fall of communism, Bulgarians and Romanians still rushed to tap foreign loans for new cars, flat-screen TVs and apartments last quarter, despite the gathering economic storm.
Bulgaria's gross domestic product (GDP), the broad yardstick for economic growth, expanded by 6.8 percent in the third quarter, well above a previous estimate of 5.6 percent, data showed on Monday. It was fuelled by an acceleration in consumption to 5.4 percent, versus 4.2 percent a year earlier.
Separate data showed final consumption in Romania jumped 13.7 percent, from 9 percent a year earlier. It was the main driver behind Romania's 9.1 percent third quarter growth.
The GDP results were only modest slowdowns from Bulgaria's 7.1 and Romania's 9.3 percent growth a quarter earlier, helping defy a trend in other ex-communist European Union peers, whose economies have lost more speed after a collapse in demand from the euro zone.
But economists said the third quarter was the last the Balkan neighbours would see of high growth for a while. They forecast a sharp deterioration that may have already begun.
"The third quarter was the last of high growth... Q4 will be bad and Q1 will be very, very bad. I see negative growth in both countries year-on-year in 2009," said Lars Christensen, chief analyst at Danske Bank.
"They were spending like there was no tomorrow and now, there is no tomorrow."
He said both countries would see a drop in the foreign direct investment needed to cover their bloated current account deficits and would suffer from a sharp decline in exports due to weaker demand in recession-hit Europe.
Austria's central bank also warned the flow of foreign funds that has fuelled the consumer boom could suddenly dry up, which could allow a crisis to spread quickly country to country.
"The risks to refinancing are increased by the danger of a domino effect, because a large part of the foreign capital in many countries comes from a relatively small number of Western European banks," the bank said in a study.
RAPID SLOWDOWN
In Romania, Ionut Popescu, a former finance minister who commentators said could return to the new centre-left cabinet after elections last month, said Bucharest may be forced to ask the IMF for at least 10 billion euros in a stand-by agreement.
Economists have said for months that Romania should seek IMF support to reassure financial markets, similar to deals sought by neighbouring Hungary and Ukraine.
Concluding a mission in Bulgaria, the IMF said Sofia had not asked for support and it did not expect it to. The government there has played down the impact of the global financial turmoil and sees 2008 growth at 6.5 percent and 4.7 percent next year.
But on Monday, the International Monetary Fund said its expansion would slam on the brakes to slow to 2 percent in 2009 and urged the country to maintain its large fiscal surpluses to underpin the currency board that pegs its lev to the euro.
"Foreign investors look at Bulgaria and they see two strengths - the currency board and the fiscal surplus. That's why it's very important to retain that surplus," IMF mission chief for Bulgaria Bas Bakker told reporters.
Sofia plans to run a budget surplus of 3.0 percent next year, but it said it may lower that to 2.0 percent to support companies and avoid a hard landing for the economy.
By comparison, most economists see Romania slowing to 4 percent, which would let it remain the EU's growth leader.
Economists say that, unlike most EU states, Romania would need to rein in state spending, particularly on welfare, to avoid economic trouble rather than stimulate flagging growth.
"Spending exuberance is very high. But it may dwindle after the Romanians realise their currency will depreciate and many redundancies will occur. We may even see a dramatic adjustment," said Ionut Dumitru, head of research at Raiffeisen in Bucharest.
Romania's leu jumped early on Monday on what dealers said was likely central bank intervention to halt a slide in the currency after designated prime minister Theodor Stolojan unexpectedly gave up his nomination and was replaced by Democrat-Liberal party leader Emil Boc. (Additional reporting by Irina Ivanova in Sofia and Radu Marinas in Bucharest; editing by Stephen Nisbet)