The German government has said numerous times since then that it would prefer to arrange a short-term loan to let Greece avoid defaulting on that payment to the European Central Bank, rather than rush through an agreement that might not prove to be durable.

At issue is whether Greece will stick to pledges to make fundamental economic changes that creditors say are needed to revive the depleted economy, including cracking down on corruption and improving tax collection. In the last few weeks, the Greek Parliament has passed more than 900 pages’ worth of new laws, containing measures like tax increases and further cuts to state spending on pensions, steps that creditors had demanded to begin discussions on the new bailout plan. Some of the measures had been promised but not put into effect by previous Greek governments.

In telephone conversations Monday and Tuesday, Mrs. Merkel told Mr. Tsipras that Germany would prefer to grant the short-term loan rather than hurry to seek approval for the broader bailout package, according to a Greek official with knowledge of the discussions, who spoke on the condition of anonymity.

“Why are you rushing?” Mrs. Merkel asked Mr. Tsipras, according to the official. Mr. Tsipras responded that talks between Greece and creditors were proceeding on the basis of the agreement struck by eurozone leaders on July 13, when both sides agreed to begin talks on a third loan program.

A spokesman for the German government confirmed that the first call had taken place but would not discuss the content. He was unable to be reached about the second call.