Updated July 10, 2015 4:25 p.m. ET
BERLIN—For Germany, offering debt relief for Greece isn’t a question of yes or no, but how much.

Officials in Germany, Greece’s biggest creditor, are mindful of a building political backlash here against five years of bailouts for Athens, which local news media and economists increasingly characterize as throwing good money after bad. That is partly why German Chancellor Angela Merkel and Finance Minister Wolfgang Schäuble frequently reject the idea of simply lopping off a chunk of the principal owed by Greece.

But Ms. Merkel, Mr. Schäuble and other German officials have also appeared at pains in recent days to leave themselves some flexibility on their position on Greece’s debt burden. They have left the door open to measures such as extending maturities or reducing interest rates on past emergency loans to Greece that would make the country’s debt more sustainable. The key question, German officials say, isn't whether Greece gets debt relief—but whether it takes enough other steps for debt relief to be a concession worth making.

Member of Parliament Eckhardt Rehberg, the spokesman for budget issues for Ms. Merkel’s conservative parliamentary group, points out that Greece is already free from debt payments for the next five years under its two past bailout programs. Instead, he said, the question is what measures Greece is willing to take to bring its fiscal house in order.

“Everyone who now focuses on this question forgets that Greece has to pay neither interest nor principal for its debt from the European rescue programs until 2020,” Mr. Rehberg said in response to a question about debt relief for Greece. “That is why currently the question is more, ‘Will I at least get to a balanced budget in Greece?’”

Athens submitted a new proposal to address its debt problems on Thursday that includes increased corporate taxes, a pension overhaul and changes to the country’s collective-bargaining system. Greece’s creditor institutions were examining the proposal on Friday as they assessed whether the country was eligible for a new bailout.

German officials have sounded a tougher line on Greek debt relief than some of Greece’s other key creditors. The International Monetary Fund says Greece needs comprehensive debt restructuring, either via a significant “haircut”—meaning a reduction in the principal Greece owes—or by significantly extending repayment deadlines. Donald Tusk, who presides over meetings of European Union leaders, also has called for “realistic” debt relief for Greece.

Germany insists a haircut would violate a European Union treaty that prohibits one country’s debt burden being shared with others Still, German officials have been careful to leave themselves wiggle room.

On Thursday, Ms. Merkel said a “classical haircut is out of the question.” But she also noted that debt relief more generally was no taboo: Greece’s creditors extended maturities and changed repayment schedules, something referred to as “debt reprofiling,” in 2012. In an appearance alongside French Finance Minister Michel Sapin on Thursday, Mr. Schäuble also cautiously left the door open to that kind of debt relief.

“We will talk about it in the coming days, but in terms of reprofiling or restructuring of debt, I’m more skeptical than Michel Sapin,” Mr. Schäuble said. Mr. Sapin has pushed for an agreement that would ease the pressure on Greece and keep it in the eurozone.

On Friday, Mr. Schäuble’s spokesman continued walking the verbal tightrope. He said Germany wouldn’t accept anything that significantly reduces the present value of Greece’s debt—without defining how great a reduction he would see as significant.

“If the intention were to reduce the present value of the debt significantly—so if we had a real loss of present value—then that would also fall under the headline of a debt haircut,” the spokesman, Martin Jaeger, said.

Write to Anton Troianovski at [email protected]