* FTSEurofirst 300 up 0.5 percent * Banks, energy stocks rebound By Tricia Wright LONDON, May 31 (Reuters) - European shares steadied on Thursday, recovering some poise after the previous session's steep losses but were still set for their worst monthly loss since August and concern over Spain's financial problems continued to weigh. The FTSEurofirst 300 was up 0.5 percent at 980.38 by 0830 GMT, having shed 1.5 percent on Wednesday, putting it on course for a monthly loss of 6 percent, its biggest since a 10.6 percent drop last August when markets were similarly beset by worries about the euro zone debt crisis. Charts painted a bearish picture for the index, which is trading below both its 21 and 200-day moving averages, and beneath the psychologically important 1,000 level. Spain's IBEX 35 rose 1 percent, but was still near nine-year lows, with the country remaining one of the primary concerns for investors as a surge in its borrowing costs fuelled worries it may not be able to fix its banking sector and may need a bailout. Attention will also be on Ireland on Thursday, as the country holds the only popular vote on Europe's new fiscal treaty, with opinion polls pointing to a 'yes' vote. "I still think there's a lot of nervousness around at the moment. We know that the situation in Europe is almost a case where it's too close to call," Henk Potts, equity strategist at Barclays, said. "The one thing we do know is there is going to be a huge amount of uncertainty - and as the old stock market saying goes, uncertainty is worse than war or famine, and that uncertainty is bound to lead to a lot of volatility." Banks limped higher on Thursday, up 0.6 percent, rebounding after four straight sessions of losses. Energy stocks also helped drive the FTSEurofirst 300's gains, bouncing after Wednesday's sharp falls as Brent crude reversed early losses to climb towards $104 per barrel, though a bleak demand outlook limited gains. "We've got some serious numbers coming out of the States this afternoon, and if they're not good, given the backdrop in Europe, it could make the situation worse," Yusuf Heusen, sales trader at IG Index, said. Financial markets were awaiting the U.S. ADP National Employment survey for May at 1215 GMT, as well as the Challenger Layoffs data for May at 1130 GMT and the latest weekly initial jobless claims at 1230 GMT, all of which will provide pointers to Friday's all-important U.S. May jobs report. U.S. preliminary first-quarter real GDP data will also be released at 1230 GMT.