European Union leaders failed to agree on a massive stimulus fund to revive their coronavirus-hammered economies on Saturday after two days of fraught negotiations but extended their summit for another day to try and overcome their differences.

As the 27 leaders scurried back to their hotels after a late, inconclusive dinner, German Chancellor Angela Merkel and French President Emmanuel Macron stayed behind in the EU’s headquarters in Brussels to haggle with the Dutch-led camp of thrifty countries demanding cuts to the 1.8-trillion-euro package...