In June, after 50 years as a bold experiment in international cooperation, the European Union appeared to be edging toward disintegration because of disputes about the European constitution, the EU budget and future enlargement.

But as EU leaders return to work in earnest this week after the summer vacation, they will be forced by their inextricable geographical ties and the continuing EU agenda of councils and meetings to rejoin the debates - and most especially to address the division caused by the loud championing by Britain's prime minister, Tony Blair, of lower-tax, low-regulation economic changes that, to his critics, seems an unforgivable assault on the cherished Social Europe of Germany and France.

It was Blair's stance and the opprobrium heaped upon him by France and Germany, that wrecked the June EU summit meeting in Brussels, a nadir for European cooperation, and prompted Blair, the current EU president, to call an extraordinary "leaders" meeting for October, which is likely to be the set-piece event of the new term.

The big question surrounds Angela Merkel, the Christian Democrat leader who, if opinion polls are right, will be Germany's chancellor after the election on Sept. 18, and whether she will beable to enact a Blairite vision. She already has appointed Paul Kirchhof, a former judge and fan of a radically simpler tax system, to campaign for her on budget and finance issues. She has dipped into the heavyweight private sector by picking Heinrich von Pierer, former chief executive of Siemens, the industrial conglomerate, as an economic adviser. The centerpiece of her program for change is a plan to cut companies' contributions to unemployment insurance, which would be paid for by an increase in the consumption tax, so German workers would be cheaper to employ. In this way, Merkel may be able to put in place changes necessary to restart the German economic motor and catch up with the faster growth of Britain.

"Merkel could make a big difference," said Paul Hofheinz of the Lisbon Council, a pro-change organization in Brussels. "She is a woman and from the east. If an outsider takes over the German political machine, that is going to be a very important event for Europe."

In France, vital signs of change are less clear. Last week, Prime Minister Dominique de Villepin announced plans to cut some taxes to increase take-home pay. But he stopped short of any big changes of inflexible French labor laws, seen by many economists as a major cause of the country's 10 percent jobless rate.

"France will always be a laggard," said Graham Watson, leader of the Liberals in the European Parliament, but, he added, the "tectonic plates are shifting in the union" as more countries come to the "recognition that protectionism does not work."

While advocates of change are gaining some ground, countries still are unlikely to agree to a deal on the EU's budget for 2007-2013, most analysts say. France will not agree to Blair's call to cut agricultural subsidies — which total around 40 percent of the EU budget — and redirect spending toward incentives for more dynamic, modern industries.

Will there be a budget deal by December?

"I don't think so,"said Katinka Barysch of the Centre for European Reform in London."Every country is under pressure to defend their national interest."

The union's political disharmony has slowed the resolution of the EU's first big foreign policy question of the new term: opening membership talks with Turkey on Oct. 3. While Britain has backed Turkish membership, skeptics such as France, Austria and Merkel in Germany toyed with the idea of delaying talks and have suggested that Turkey be given partnership status, not full membership.

They have concerns about a new wave of immigration and jobs competition, concerns inflamed by the cultural shock that was caused when 10 new countries, mainly from central and eastern Europe, joined the EU in 2004. But there is an additional visceral opposition toward allowing a large, poor Muslim nation to join a mainly Christian club. The talks are likely to start on time, but the ill-will shown by the warring Europeans has dented Turkey's enthusiasm and the negotiations are likely to be long and fractious

"Turkey has been trying to join for 40 years, but people are now thinking about a period when relations with the EU will be frozen or put on the side," said Suat Kiniklioglu, director of the Ankara office of the German Marshall Fund of the United States. "They think this process will not end with membership or a solution that is satisfying to Turks."

A bulwark against the further loosening of cooperation among EU states could be the European Commission, the Brussels executive body that traditionally holds center ground against the forces pushing member countries apart. But the commission under José Manuel Barosso, its president, has had a series of setbacks in the past year. It had to change the rules of the stability and growth pact, a mechanism designed to rein in countries' wayward borrowing, when Germany and France broke them. It had to backtrack on a plan to deregulate Europe's services sector, again under French-German pressure. Now the commission is mired in a row about Chinese textiles imports after it put in place a quota system that has caused an embarrassing pile-up of clothes at Europe's borders.

"The biggest problem right now is we have a weakened European Commission," said Hofheinz of the Lisbon Council. "The ability of the Brussels institutions and the commission in particular to stand up to the member states has been systematically ripped apart."