* Spain sells 3.1 billion euros of new 9-month bill
* Yields down 20 basis points on the 3-month bill
* Auction comes before triple-bond sale on Thursday
MADRID, Feb 19 (Reuters) - Spain sold another 4 billion euros ($5.3 billion) in short-term debt on Tuesday, borrowing the maximum it had targeted ahead of a triple bond auction on Thursday.
The sale, focusing on a new 9-month bill, adds to a flood of borrowing by the countries at the centre of the euro zone's debt crisis at the start of this year, facing down nerves around Italian elections at the end of this week.
The Treasury sold 3.1 billion euros of the new 9-month bills, which replace 18-month debt, at an average yield of 1.144 percent and a bid-to-cover ratio of 2.3.
It also placed 886 million euros of 3-month bills at an average yield of 0.421 percent, slightly lower than the 0.441 percent when it last sold in January.
"Despite the mounting political and economic risks, and increasing concerns about the relatively high level of issuance, demand for Spanish paper continues to hold up and sentiment remains favourable," said Nicholas Spiro, managing director of Spiro Sovereign Strategy in London.
Investor concerns over Spain's finances have eased since the European Central Bank said it would buy the debt of struggling countries seeking help last summer.
Madrid is likely to report a budget shortfall of around 7 percent of gross domestic product for 2012, above an EU target though Brussels has applauded government efforts to keep down the deficit in the face of a deep and prolonged recession.
A corruption scandal involving the leading People's Party and the upcoming election in fellow struggler Italy has also failed to dampen investor appetite.
The premium bond traders demand to hold Spanish over German debt stood at around 360 basis points on Tuesday, a long way from euro-era highs last July of over 650 basis points.