* FTSEurofirst 300 up 1.2 percent
* Alcoa's results, Siemens's outlook fuel earnings optimism
* Euro zone debt crisis concerns recede on Portugal comments
By Harpreet Bhal
LONDON, Jan 11 (Reuters) - European shares rose on Tuesday as a strong start to the U.S. earnings season boosted optimism about upcoming company results, and reassuring comments from Portugal soothed nerves over the sovereign debt crisis.
The pan-European FTSEurofirst 300 index of top shares closed up 1.2 percent at 1,147.15 points, hovering near the highest closing level since mid-September 2008.
Forecast-beating results overnight from U.S. aluminium company Alcoa set a positive tone for the start of the corporate earnings season, ahead of the release of results from Intel and JPMorgan Chase later this week.
In Europe, German conglomerate Siemens rose 3 percent after saying its first-quarter profit and sales were set to surpass the year-earlier figures on robust factory demand.
"All the leading indicators are pointing towards a positive earnings season once again," said Lothar Mentel, chief investment officer at Octopus Investments, adding that markets could push higher "as long as the positive results are accompanied by half decent outlooks".
Heavyweight banking stocks rebounded from falls in the previous three sessions, with HSBC and Credit Agricole both up 2.4 percent following recommendation upgrades from brokers Citigroup and Societe Generale respectively.
Barclays rose 5.5 percent as BofA Merrill Lynch added the stock to its "Most Preferred List" and Societe Generale said the bank was among its top picks in the European sector.
Technology stocks were also in demand, led by gains in Britain's ARM Holdings which rose 7 percent as bid speculation circulated around the chip designer.
"ARM is higher again today after last week's news of a tie-up with both Microsoft and graphics card company Nvidia. Further bid speculation has also helped the shares rise in price today," said Michael Hewson, market analyst at CMC Markets.
PORTUGAL AUCTION EYED
Helping calm some nerves over the euro zone debt crisis ahead of a bond auction on Wednesday, Portuguese Prime Minister Jose Socrates said Lisbon had no plans to seek aid after what he said were "excellent" budget execution results for 2010.
Investors also took comfort from news that Japan was considering buying about 20 percent of euro zone bonds to be jointly issued later in January to raise funds to support debt-swamped Ireland.
"The news will surely have a calming effect on bond markets today," analysts at Commerzbank wrote in a note, adding that although Asian support may be positive in the short term, it by no means guarantees restoring investor trust in the market.
On the downside, retailer Marks & Spencer fell 2.8 percent after saying cold weather hurt Christmas sales, and warned of tough trading ahead due to squeezed households and rising commodity prices.
German retailer Metro AG, which also said snow and ice hit fourth quarter demand, shed 0.8 percent.
Actelion lost 1.7 percent as the biotech firm warned after markets closed on Monday that full-year earnings before tax (EBIT) growth would miss its guided range.
Across Europe, Britain's FTSE 100, Germany's DAX and France's CAC 40 rose 1 to 1.6 percent, while the Thomson Reuters Thomson Reuters Peripheral Euro Zone index added 1.5 percent. (Editing by Hans Peters)