* Merkel says Greece is euro zone's responsibility
* EU leaders to discuss Greece at summit
(Adds quotes)
By Sarah Marsh
BONN, Germany, Dec 10 (Reuters) - German Chancellor Angela Merkel showed solidarity with Greece over its debt problems on Thursday, saying countries in the euro zone had a collective responsibility for the country's fate.
She did not say what common responsibility would mean in terms of any action over Athens' difficulties, but said the subject would be discussed at a summit of European Union leaders later on Thursday in Brussels.
"What happens in one member state affects all others, especially as we have a common currency, which means we have a common responsibility," Merkel told a news conference.
Greek debt and stock prices have taken a beating after a downgrade from rating agency Fitch this week because of the country's huge budget deficit and public debt.
The 10-year Greek/German yield spread
"I am certain that we will discuss the situation of Greece at our meeting later this afternoon. I talked about the Stability and Growth Pact during my speech and this is what we are using as a basis," Merkel told reporters after addressing centre-right party leaders in Bonn before the EU summit.
The Stability and Growth Pact is a set of EU rules limiting government deficits to 3 percent of GDP and debt to 60 percent of GDP. The executive European Commission sees the Greek budget deficit at 12.7 percent this year and debt at 112.6 percent.
To put its public finances on a sustainable path, Athens needs to launch structural reforms, primarily of its pension system, as it faces one of the biggest fiscal challenges in Europe from the ageing of its population.
Greek Finance Minister George Papaconstantinou said on Tuesday the government would submit such a bill to parliament in the summer, but some economists expect strong public opposition to such reforms.
Yet without reforms Greece is unlikely to be unable to respect the EU budget rules, which were designed to limit government borrowing and underpin the common euro currency.
In her speech to centre-right party leaders Merkel said a key question for the EU was the tenuous relationship between national social policies and the uniform European economic and monetary policy.
"If, for example, there are problems with the Stability and Growth Pact in one country and it can only be solved by having social reforms carried out in this country, then of course the question arises, what influence does Europe have on national parliaments to see to it that Europe is not stopped," Merkel said.
"This is going to be a very difficult task because of course national parliaments certainly don't wish to be told what to do. We must be aware of such problems in the next few years." (Reporting by Sarah Marsh, writing by Jan Strupczewski; Editing by Andy Bruce)