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Greek uncertainty curbs European stock gains

* FTSEurofirst 300 index closes up 0.6 pct

* Athens bourse falls, hit by ongoing political uncertainty

* Upbeat economic news lifts Madrid and Lisbon markets

* FTSE up but pares gains as UK external deficit rises

By Sudip Kar-Gupta

LONDON, Dec 23 (Reuters) - A fall in Greek stocks kept a lid on gains in European equities on Tuesday, as the Athens bourse was hit by the prospect of early elections that could put Greece's rescue package at risk.

The pan-European FTSEurofirst 300 index closed up 0.6 percent at 1,374.80 points, with the index up 4.4 percent since the start of 2014.

The broader European equity landscape was helped by positive economic news from Spain and Portugal.

The Bank of Spain raised its economic forecast while Portugal's budget deficit shrank.

However, Athens' benchmark ATG equity index underperformed due to uncertainty over Greek politics. The ATG, which dropped nearly 20 percent in the second week of December, ended 1.7 percent lower.

The Greek parliament on Tuesday failed to elect a new president in a second-round vote. It has one more chance to do so next week to avert elections that could bring to power a party that wants to renegotiate the country's bailout deal, end years of austerity and write off some Greek debt.

Prime Minister Antonis Samaras, whose term is not due to end until mid-2016, has offered to bring pro-European independents into government and hold elections by late next year if they support Stavros Dimas, the only candidate in the presidential race.

"With many analysts predicting that Greek MPs will fall short of the votes needed to support presidential candidate Stavros Dimas, more destabilisation could be on the way for Greece, and by extension, the euro zone," said Spreadex financial analyst Connor Campbell.

Across Europe, Britain's benchmark FTSE 100 closed up 0.3 percent, Germany's DAX rose 0.6 percent while France's CAC advanced 1.4 percent.

Portugal's PSI-20 equity index outperformed to rise 1.8 percent after the reduction in Portugal's budget deficit, while Madrid's IBEX also advanced 1 percent after the Bank of Spain forecast faster economic growth.

However, the FTSE ended off its intraday highs after data showed Britain's deficit with the rest of the world had risen to 27 billion pounds ($42 billion), equivalent to 6.0 percent of gross domestic product (GDP), matching the biggest deficit on record.

"The UK current account data has triggered some sell orders," said AvaTrade chief market analyst Naeem Aslam.

($1 = 0.6423 pounds)

Europe bourses in 2014:

Asset performance in 2014:

Today's European research round-up (Additional reporting by Blaise Robinson; Editing by Dominic Evans)