German Chancellor Angela Merkel's ruling coalition will back Greek aid because the euro's future is at stake, but Greece must first prove it is tackling its budget deficit, a senior official in her party said.

We said we would help if the euro's stability is at stake, we're now in that situation, Volker Kauder, parliamentary floor leader of Merkel's Christian Democrats (CDU), told German television station ARD.

However, firstly we need to check carefully that Greece is pressing ahead with its deficit cuts. It's not going to be handed over on a silver plate, he said. We'll have to help, but the conditions for that have not yet been met, he added.

Public opposition to a bailout for debt-stricken Greece is widespread in Germany, and Merkel has consistently pursued a tough line on offering potential aid.

Kauder said he expected the ruling coalition of conservatives and pro-business Free Democrats (FDP) would back any financial support for Greece in parliament.

If the conditions are met, we'll do it. The chancellor has always said the last resort would be when the stability of the euro is in danger. I think we'll get the majorities in the coalition then, Kauder added.

Germany's opposition Social Democrats (SPD) have threatened to delay efforts to accelerate the legislative process of approving any aid, and a senior member of the party said on Monday it was important that any bill was properly discussed.

The SPD's Petra Merkel, who heads the budgetary committee of the Bundestag lower house of parliament, told ARD it was important to hold a transparent public debate on Greek aid.

Asked whether her party, whose votes would not be needed to get a bill through parliament, would block aid, she said:

We won't reject it. We're going to look at exactly what's possible and what alternatives there are, she said. I also think we're likely to take the view that we'll have to help.

It was vital that aid for Greece did not encourage other debt-laden euro zone members to follow suit, she added.

The SPD could slow down the parliamentary process by demanding committee hearings to discuss the aid.

German Finance Minister Wolfgang Schaeuble is due to meet parliamentary leaders in the coalition on Monday to discuss the euro zone/International Monetary Fund aid package for Greece, of which Germany could shoulder up to 8 billion euros.

(Reporting by Dave Graham; Editing by Toby Chopra)

Germany