* FTSEurofirst 300 flat after near 6 pct rally in 5 days
* All eyes on size, details of expected ECB stimulus programme
* Euro zone stocks at 50-year low vs US stocks -BofA-Merrill
* Greek banks bounce as emergency line granted
By Blaise Robinson and Francesco Canepa
PARIS/LONDON, Jan 22 (Reuters) - European shares paused on Thursday after a sharp five-day rally as investors waited to see the size and shape of a bond-buying programme the European Central Bank is expected to unveil later.
Euro zone banks have been among the top gainers ahead of today's ECB meeting, with Societe Generale, UniCredit and Mediobanca all up about 11 percent in the past week, and ING up 8.2 percent.
Market expectations are sky-high for the ECB to announce large-scale government bond purchases with new money, or quantitative easing although its exact size and duration are still unclear.
"QE itself is in the market except its size and how long it will last," said Markus Huber, a senior trader at Peregrine & Black. "Anything less than 500 billion euros would be definitely a disappointment (and) if it's just a year, that's also already in the market."
At 1120 GMT, the FTSEurofirst 300 index of pan-European shares was down 0.04 percent at 1,430.55 points, hovering just below a seven-year high hit earlier in the session.
The benchmark index has risen nearly 6 percent in the past five sessions, strongly outpacing U.S. equity markets.
European stocks still trade at relative multi-year lows versus U.S. shares, and many analysts expect the gap to start closing as investment flows return to Europe.
While Wall Street's benchmarks recently hit record highs, the euro zone's blue-chip Euro STOXX 50 still needs to rally by about 40 percent to reach 2007 peaks.
In terms of relative price performance, euro zone stocks trade at a 50-year lows versus U.S. stocks, according to Bank of America-Merrill Lynch.
European stocks also look cheap with earnings factored in, trading at the lowest price-to-earnings ratio to the U.S. market in 2-1/2 years, Thomson Reuters Datastream figures show.
Giant fund manager Pimco, which has $1.68 trillion in assets under management, said on Tuesday it has placed an 'overweight' position on global equities, particularly European stocks.
Britain's FTSE 100 index was up 0.3 percent on Thursday, Germany's DAX was down 0.2 percent and France's CAC 40 was 0.1 percent lower.
Greek banks rose 1.3 percent after a banking source told Reuters late on Wednesday the ECB had approved an emergency funding line for Greek banks to be provided via the national central bank.
Logitech surged 10.3 percent as the Swiss maker of computer peripherals said it was raising its guidance for full-year operating income.
Today's European research round-up (Editing by Catherine Evans)