BRUSSELS (Reuters) - European Union leaders are set to end weeks of wrangling over top jobs in Brussels and agree on Saturday on who will fill key posts in EU institutions that face major challenges from a combative Russia and a stuttering economy.

A summit in Brussels that was called after a pre-vacation meeting two months ago ended in deadlock is likely, diplomats and officials said, to hand Poland’s conservative prime minister the influential role of European Council president and Italy’s little tested young foreign minister given the running of the EU’s common diplomatic efforts. But nothing is yet certain.

Russia’s assumed military intervention in Ukraine will also be discussed when the prime ministers and presidents meet from late afternoon, but officials doubt they will do more than agree to study stepping up their economic sanctions on Moscow.

EU foreign ministers meeting in Milan on Friday spoke of toughening an arms embargo, extending the list of individuals or sectors targeted by economic sanctions and also of sending military equipment to Ukraine.

Ukrainian President Petro Poroshenko will be in Brussels on Saturday, aiming to persuade the EU to do more to deter Russian President Vladimir Putin from supporting separatist rebels.

But while former Soviet satellite states in the east are keen for tougher measures, the western powers, notably Germany, France, Italy and Britain, fear damaging their own fragile economies by losing Russian business - and are even warier of risking an interruption in Russian gas supplies this winter.