3 MIN. DE LECTURA
* FTSEurofirst 300 up 0.2 pct, rises for 5th day
* Erases early losses on ECB stimulus speculation
* Greek shares fall as Syriza party extends lead
* SGS down 7 percent after cutting growth targets
By Francesco Canepa and Blaise Robinson
LONDON/PARIS, Jan 21 (Reuters) - European shares edged up in nervous, choppy trade on Wednesday as speculation mounted about the size and timing of a sovereign bond buying programme expected to be unveiled by the European Central Bank (ECB) this week.
A euro zone source told Reuters on Wednesday the ECB's Executive Board has proposed that the bank buy 50 billion euros ($58 billion) in bonds per month from March.
The FTSEurofirst 300 index of top European shares erased its losses after the report to trade 0.2 percent higher at 1,425.45 points at 1545 GMT. The index briefly traded as much as 0.5 higher.
"(The 50 billion-euro figure) at a minimum, meets expectations," Dan Greenhaus, chief strategist at BTIG, said. "(But) If this means the ECB is considering, or would implement, an open-ended form of QE (quantitative easing), well then that's a whole other ballgame."
The FTSEurofirst, which hit a seven-year high on Tuesday, surged 5.5 percent in the previous four sessions on expectations the ECB would announce sovereign bond purchases.
Money market traders polled by Reuters say the European Central Bank is expected to announce on Thursday a 600 billion euro sovereign bond-buying programme, known as quantitative easing.
Athens' main equity index underperformed, falling 2.4 percent after a survey showed that political party Syriza, which is running on pledges to end austerity policies and renegotiate Greek debt, has widened its opinion poll lead over the ruling conservatives.
Trading volume in Greece remained 25 percent below the index's full-day average for the past three months.
"We expect the market to remain nervous as the election date draws nearer, with light volumes to persist," analysts at Euroxx Securities in Athens wrote in a note.
Elsewhere, shares in Switzerland's SGS dropped 6.6 percent after the world's largest testing and inspection company cut its outlook for revenue and margins. Peer Intertek fell 4.2 percent. (Editing by Mark Heinrich and Elaine Hardcastle)