Mrs. Merkel’s leadership has come at a high cost for indebted countries, especially those on the periphery, with cuts in public spending biting just as joblessness has surged. Youth unemployment in Spain is nearly 50 percent, a fact Mrs. Merkel raises with domestic audiences when cautiously selling more intervention.

The treaty changes she and President Nicolas Sarkozy of France proposed in Paris on Monday would have been inconceivable at the beginning of the crisis, since it requires states to cede a significant degree of economic sovereignty. It is a process that many observers, in particular the populist British press, say is well underway. German dominance of the euro zone, they say — with Mrs. Merkel as the unofficial but unchallenged leader of Europe — has in fact already arrived.

Silvio Berlusconi’s resignation as Italy’s prime minister was interpreted as an omen for Europe’s German-directed future. And confidential draft proposals of Ireland’s December budget were found to have circulated among lawmakers in Berlin last month before opposition lawmakers in Dublin saw them.

Despite her global prominence, Mrs. Merkel, an East German physicist turned politician, cuts a modest figure in Berlin. She still lives with her media-shy second husband, a quantum chemist, in the same apartment in the central Mitte District that they lived in before she became chancellor. Her daily commute carries her across the former path of the Berlin Wall, a reminder of her years trapped behind it.

The future of the European Union could well be decided at this week’s summit meeting in Brussels. But a routine day in Mrs. Merkel’s schedule here in the German capital illustrates the unique demands on her, as both a leader who is the unlikely fulcrum of the world’s financial future and as someone who must play the role of legislator and party leader.

Last week, she gave a closely watched government address in the historic Reichstag building, where she compared the steps to strengthen the 17-member currency zone to a marathon.

Mrs. Merkel is not a charismatic speaker but she possesses a commanding air. At one point, a buzz of chuckles and chatter rose from the ranks of the opposition Green Party. Mrs. Merkel looked up from her notes, cast a glare at the murmuring politicians seated before her and said, “It appears to be incredibly funny to the Greens. To me, it’s incredibly logical. That’s just the difference.”