* Presidential vote sparks widespread market jitters
* Investors worry Syriza government would push to write down debt
* Sell-off may continue for weeks, say analysts (Updates prices, adds fresh analyst comment)
By John Geddie
LONDON, Dec 10 (Reuters) - Greece's short-term borrowing costs climbed above long-term rates on Wednesday, a sign that investors fear political upheaval in Athens could push the country back towards default.
The move follows a sell-off on Tuesday after Greek Prime Minister Antonis Samaras brought forward a presidential vote, a gamble that could end up catapulting into power the leftist party Syriza, which opposes Greece's bailout agreement.
Bondholders would prefer a pro-business government that will stick to the IMF/EU bailout programme, which has been extended until early next year.
Yields on Greek three-year bonds jumped over 130 basis points to 9.85 percent, the highest since the bonds were issued in July. Ten-year yields rose just 65 basis points to 9.025 percent. (http://link.reuters.com/zuj63w)
"This inversion tells you that there is concern about further potential debt writedowns, and that is a function of minds being focused on Syriza, which would no doubt push hard for such a policy," said Rabobank strategist Lyn Graham-Taylor.
Syriza holds a five-point lead over the ruling conservatives, according to the first poll published since Samaras moved up the presidential vote.
Credit Suisse analysts put the chances of an early general election at better than 50 percent.
The cost of buying protection against a Greek default using a five-year credit default swap rocketed 100 bps, CDS prices from Markit showed.
Greece agreed a debt swap deal with its creditors in 2012 in exchange for receiving the second tranche of its 240 billion euro bailout.
Most of its outstanding debt - which is around 175 percent of GDP - is held by the official creditors, but analysts say that may not protect private investors from any future debt restructurings. Athens issued five- and three-year bonds in the capital markets earlier this year, its first since default.
The political uncertainty has shaken other markets, from Greek stocks to other lower-rated euro zone bonds. If Samaras fails to secure support for his presidential candidate, snap elections could be called that Syriza would be likely to win.
Portuguese 10-year yields were 14 bps higher at 2.98 percent. The Italian and Spanish equivalents rose 6 bps to 2.08 and 1.88 percent. Athens was the worst-performing stock market in Europe.
German bonds, which fall in times of uncertainty as investors seek refuge in top-rated assets, dipped 1 bp to a record low of 0.673 percent.
The EU's economics chief tried to quell market fears on Tuesday, saying Samaras's decision to bring forward the vote showed he was confident he could win.
But with the vote to be held over three rounds, and the government most likely to win at its last attempt on Dec. 29 where it requires a smaller majority, market jitters are likely to continue in the weeks ahead.
"Usually ... with yields at these levels, some value investors could step up and take a risk, but it doesn't look likely, especially as ... we have to wait until the 29th," Commerzbank strategist David Schnautz said. "So there could be a free fall in Greek bond prices before any of those investors step in." (Additional reporting by Emelia Sithole-Matarise; editing by Andrew Heavens, Larry King)