* Treasury to sell 3.5-4.5 bln euros in 3 bonds
* Will sell a bond maturing 2032
* Successful long-term bond sale may help delay call for aid
* Aid request still seen inevitable by analysts
* Auction should complete 2012 debt issuance plans
By Nigel Davies
MADRID, Nov 8 (Reuters) - Spain will test appetite for its longer-term debt on Thursday for the first time in a year and a half, and decent demand could give it some leeway to delay a request for a European bailout as its borrowing needs for the year would be met.
The Treasury aims to sell between 3.5 billion euros ($4.5 billion) and 4.5 billion euros of debt, and can be expected to sell most of that in two bonds maturing in 2015 and a new five-year bond.
But the market will be looking at how much the Treasury sells of a bond maturing in 2032, an indication of what interest there is in longer-term investment in Spain. Spain has not sold such a long-dated bond since May last year, before the financial crisis took a turn for the worse.
Spain has been able to delay a request for international aid as its debt costs have fallen sharply since the announcement of a European Central Bank bond buying scheme intended to help struggling euro zone countries.
A successful auction on Thursday could allow Prime Minister Mariano Rajoy to delay requesting a rescue package still further, even if analysts see such a call as only a matter of time.
"There is concern that even if Spain has access to markets and shows there is demand for its longer-term debt, that yields are still are at unsustainable levels. Spain cannot issue at these levels indefinitely," said Orlando Green, strategist at Credit Agricole.
He said a request for a rescue package could be delayed until after elections in the economically important region of Catalonia on Nov. 25, or even into next year.
Spain could also be persuaded not to move quickly on a request for aid because a successful auction would finish off the Treasury's planned bond issuance for this year, leaving it to concentrate on funding needs for 2013 with two months of the year remaining.
That will give it a headstart on funding in a year when analysts expect the economy to contract by around 1.5 percent, around the same as predicted this year, and with financing needs stacking up for the country's autonomous regions.
Analysts said there was demand from investors for the 20-year bond, indicating the Treasury should not experience problems selling the debt.
However, they were reluctant to say how much the Treasury would need to sell for the sale to be deemed a success. On Wednesday, the bond had a yield of around 6.3 percent on the secondary market, giving some indication of where it would be on Thursday.
The Treasury has reported an uptick in foreign demand at Spanish debt auctions as the ECB's bond plan has provided some sort of backstop for the country's debt issuance.
"We are seeing good appetite for Spanish paper and there is no reason to think that won't be the case on Thursday," said Peter Goves, an analyst at Citi.
The spread between the yield on Spain's ten-year government bond and that of benchmark German bunds was around 430 basis points late on Wednesday, more than 200 basis points down from record highs hit in July.
The shorter dated bond maturing in 2015 should have a yield of around 3.6 percent, while the new five-year bond was trading at around 4.6 percent on the grey market.