Spain to test market status with long-term bond sale

* Treasury to issue up to 4 bln eur of 10-, 30-yr bonds

* Long-term debt issue follows strong T-bill auction

* Auction results due at around 0840 GMT MADRID, May 19 (Reuters) - Spain is likely to have little trouble in selling 10- and 30-year bonds on Thursday, though borrowing costs may rise compared with previous similar auctions as Greece's debt burden keeps markets nervous.

Spain's Treasury plans to auction between 3 billion and 4 billion euros ($4.3 billion-$5.7 billion) of debt expiring in 2021 and 2041, just two days after issuing 5.5 billion euros of short-term T-bills.

The euro zone's fourth largest economy, Spain has driven through austerity measures and reforms to convince markets it will not need to follow Greece, Ireland and Portugal in seeking a bailout.

"The 10-year (Spanish) bond is quite attractive at the moment. I expect mostly domestic investors to support the 30-year issue while there will also be foreign interest for the 10-year bond," Ioannis Sokos, rate strategist at BNP Paribas said.

"The timing is also good, because the Ecofin gave some positive signals with the Portuguese packet finalised ... and if anything we are in a better shape than we were three weeks ago on the Greek story." European finance ministers agreed a 78 billion euro aid package for Portugal on Monday and broke a taboo on Tuesday to acknowledge for the first time that Greece may have to restructure its debts, a risk markets have long anticipated.

Spain's gross domestic product is double that of Greece, Portugal and Ireland combined, piling pressure on euro zone policymakers to stop Madrid getting sucked into the bloc's debt crisis.

A big public deficit and uncertainty over bank capitalisation levels after a property sector collapse have kept the yields on Spanish bonds around 200 basis points above benchmark German Bunds, well above the pre-crisis premium of around 50 bps. ES10YT=TWEBDE10YT=TWEB

The 10-year bond, which carries a coupon of 5.5 percent, was trading at around 5.3 percent on the secondary market on Wednesday, down from an average yield of 5.472 percent when it was last auctioned on April 20.

The 30-year bond with a 4.7 percent coupon was trading at around 5.9 percent on Wednesday compared with an average yield of 5.875 percent at its last auction March 17.

Spain has already issued 38.7 billion euros in medium and long-term debt this year out of the initially projected 93.8 billion euros of bonds targeted by the Treasury's 2011 debt strategy. (Reporting by Paul Day; Editing by Ruth Pitchford)