* Yield climbs to 3.403 pct vs 1.818 pct on Nov. 3
* Below secondary market level, demand seen strong
* Sells all 500 mln euros on offer
(Adds economist, government meeting)
By Andrei Khalip
LISBON, Dec 15 Portugal's three-month borrowing costs nearly doubled at its last debt auction of the year, reflecting persistent investor concerns about the debt-ridden country, though the rise was smaller than traders had expected.
While the yield of 3.403 percent marked a euro lifetime high and a huge leap from 1.818 percent at the previous auction on Nov. 3, it came in below secondary market rates of around 3.8 percent on the same maturity PTEGE0011=TWEB.
Traders had been expecting a yield of 3.5-3.8 percent.
"This is not that bad if you look at the secondary market yields. Obviously it is relatively weak, but at least it is not going to leave the market worried again about funding," said Orlando Green, debt strategist at Credit Agricole in London.
"I think the main concern though is that the market will be tougher next year. We are holding on to see the sentiment in January," he added.
Portugal sold all 500 million euros ($670.8 million) worth of March 2011 T-bills on offer, and demand -- relatively strong for the year-end pre-holiday season -- outstripped supply by 1.9 times, slightly lower than 2.2 times at the previous auction.
Portugal's borrowing costs have spiked this year on investor concerns over its public finances, and more recently, over the possibility that it may follow Ireland and Greece in seeking outside help to manage its debt.
Most analysts said the auction did not raise the pressure on Portugal to consider the option of a bailout, but neither did it ease such concerns.
"It was an expected yield rise, so I think it does not put more pressure on Portugal to ask for assistance. But it remains a fairly high yield and if it remains at these levels it will force the government to cut spending further," said Joao Sousa, an economist at BPI bank in Lisbon.
The cost of short-term money has risen even as the European Central Bank has moved to keep a lid on benchmark 10-year debt yields in the past two weeks.
The premium investors demand to hold Portuguese 10-year-bonds rather than safer German Bunds rose about 5 basis points on Wednesday afternoon to 358 bps from Tuesday's settlement levels.
The government has promised to Brussels it will slash the budget deficit to 4.6 percent of gross domestic product next year from this year's estimated 7.3 percent, and it has introduced painful austerity measures such as a 5 percent cut in civil servants' wages, as well as tax hikes in the 2011 budget.
European Union Monetary Affairs Commissioner Olli Rehn told the European Parliament on Wednesday that Portugal and its bigger neighbour Spain, which has also been viewed with nervousness by investors, were taking very convincing fiscal consolidation measures.
The cabinet, which was in a weekly meeting on Wednesday, is also expected to announce this week a range of measures to help secure economic growth and boost competitiveness. These will include measures for the labour market and steps to reduce red tape and bolster exports.
The government expects the economy to grow at least 1.3 percent this year on the back of rising exports after a 2.6 percent contraction in 2009.
Next year, it hopes to eke out a 0.2 percent expansion as it expects strong exports to outweigh the impact on domestic demand of painful austerity measures.
But many economists expect the country to slide into a new recession, which would make the task of meeting the deficit target much tougher to reach.
Portugal has now completed its debt issuance programme for 2010. Its next bond redemption is not due until April, when it has to repay 4.5 billion euros. In total, Lisbon has to repay 9.5 billion euros in bonds next year.
According to the Portuguese 2011 budget, next year's net financing needs are 10.75 billion euros. (Additional reporting by Shrikesh Laxmidas and Filipa Lima; Editing by Hugh Lawson)