Prolonged German downturn could prompt stimulus rethink

(Repeats story filed overnight without changes)

* String of weak data raise questions about German strength

* Stimulus shift could occur if budget goal looks out of reach

* IMF, ECB and EU partners call on Berlin to loosen fiscal reins

* Economists estimate annual investment gap at 80 bln euros

By Noah Barkin

BERLIN, Oct 8 (Reuters) - The last thing the faltering European economy would appear to need right now is a sudden downturn in Germany, hitherto the bloc's pillar of strength.

But a bout of German weakness may be precisely what is required to convince Angela Merkel to loosen the fiscal reins at home and provide Europe with a dose of stimulus that struggling states like France and Italy have long been seeking.

For now, the top economic priority of Merkel's government is to deliver on its promise of a "schwarze Null" - a federal budget that is in the black, or fully balanced - in 2015.

That goal, spelled out in the coalition agreement struck last year between Merkel's conservatives and the centre-left Social Democrats (SPD), is described by officials in Berlin as a political "holy grail" - an historic achievement that would carry huge benefits for both ruling partners if reached.

It is largely due to the constraints of this budget target that Merkel has repeatedly rebuffed calls at home and abroad for Berlin to splash out more public money on infrastructure.

But if the German economy, which contracted by 0.2 percent in the second quarter and may flatline in the third, continues to weaken into next year, Merkel could be forced to reverse course and step up public investment, as the European Central Bank (ECB) and International Monetary Fund (IMF) have urged.

"If the only way to achieve the balanced budget goal is to make cuts that would deepen a recession, it will be abandoned and we will see more spending," said one senior German official, who requested anonymity due to the sensitivity of the issue.

Another official close to the chancellor said: "If the German economy weakens substantially, that would be a game changer."

POOR DATA

For now, the "schwarze Null" - or black zero - looks comfortably within reach.

With unemployment still hovering near post-reunification lows under 7 percent, tax revenues continue to flow into federal coffers at record rates.

Rock-bottom interest rates have sharply reduced the cost of borrowing in Germany, providing additional budget support. The Bundesbank estimates the German state saved 120 billion euros over the past seven years - including 37 billion euros last year - thanks to the drop in rates.