* Kremlin aide says budget deficit may top 6 percent in 2010
* State to spend 0.5 percent of GDP on banks' capital-Kudrin
* Alfa Bank, Fitch bearish on bad loans
* Railways head says more nationalisations needed
By Darya Korsunskaya and Toni Vorobyova
MOSCOW, June 30 (Reuters) - Russia's budget deficit could top 6 percent of economic output in 2010 because the country needs to recapitalise banks that are struggling with bad loans, officials said on Tuesday.
A top banking executive and ratings agency Fitch suggested that prognosis might be too optimistic because banks may need 10 times as much cash as the 210 billion roubles ($6.75 billion) or 0.5 percent of gross domestic product officials suggested.
Fitch said Russian corporations may default on as much as $130 billion in loans.
Russia could cut rates by a further 150 basis points in 2009, a central bank official said, to revive bank lending and prevent the slowdown from stretching into 2010 and beyond.
"If prices for oil and natural resources do not sharply rise... then the deficit in 2010 will be more than 5 percent and likely even more than 6 percent of GDP..." the Kremlin's top economic aide Arkady Dvorkovich told reporters.
Energy taxes constitute the lion's share of state revenues and a plunge in oil prices forced Russia to recalculate its 2009 budget at $41 per barrel from the previous $95, which resulted in an 8 percent deficit of around $113 billion.
Russia had hoped for a deficit of 5 percent in 2010 and Prime Minister Vladimir Putin has said Russia cannot afford a deficit of 13 percent -- an indirect reference to the United States, which may run a deficit of $1.43 trillion next year.
With Russia battling its first recession in a decade and foreign capital markets still virtually closed off in the aftermath of the global credit crunch, its banks are under increasing pressure to support the economy.
"The banking sector needs up to 10 percent of GDP, otherwise we won't restart," said Peter Aven, the head of Russia's top private bank Alfa Bank.
"Enterprises could well not redeem $130 billion of their core debt. Bad loans of some 25-30 percent (of the total portfolio) by the end of the crisis is a reality today," Aven, known for his bearish views, told a conference.
Alexander Danilov, senior director at Fitch's Russian office, said Russian banks may need between $20 billion and $80 billion in extra capital this year.
Standard and Poor's has said problem loans could soar to 35-50 percent of total lending in Russia, Ukraine and Kazakhstan, though actual loan losses would not be more than half that level in Russia.
'NOT LITTLE GIRLS'
Putin told state banks on Monday to boost the economy with up to $16 billion in loans and ordered bank heads "not to plan any summer holidays".
Stalled lending is seen among the key problems for the economy which is now poised to shrink 8.5 percent this year after years of an oil-fuelled boom.
Russia, which has the world's third largest reserves of over $400 billion, has filled this year's budget gap with windfall oil money accumulated over the past years of economic boom.
Next year's deficit will already require borrowing and the country plans to issue up to $10 billion in Eurobonds. Deputy finance minister Dmitry Pankin said over $30 billion could be also borrowed from the local rouble market next year.
Russia's deep downturn has pushed the jobless rate to a 9-year high of around 10 percent and potential public unrest remains the key challenge for Putin.
The head of state railways, Vladimir Yakunin, whose monopoly is Russia's biggest employer with 1.2 million people, called on Tuesday on the government to nationalise struggling industries:
"We see in the anti-crisis measures of other countries that they are not little girls. If they need to save private banks, they nationalise them. If they have to support some industrial sector, they don't just throw money at it, they nationalise it".
(Additional reporting by Yelena Fabrichnaya, Simon Shuster and Oksana Kobzeva, writing by Guy Faulconbridge and Dmitry Zhdannikov; Editing by Ruth Pitchford)