Danish Prime Minister Anders Fogh Rasmussen said the coming half-year would be "historic" and high-risk, as member states must reach agreement on the terms of EU expansion by the end of the Danish presidency in December if enlargement is to meet the 2004 timetable set by EU leaders.
Rasmussen celebrated the start of the Danish presidency late on June 30, inviting European Commission President Romano Prodi and other EU officials to a garden party in Copenhagen's Tivoli gardens.
The Danish leader said his government was "determined to respect the set timetable and to conclude negotiations before the Copenhagen summit in December, because any delay, of even a few months, would set back candidate countries' entry into the EU by several years."
A failure to meet the deadline would be "a historic mistake that Europe cannot allow," Rasmussen said, adding that "the verdict of posterity would be severe for those responsible for blocking enlargement."
The Danish government has not hesitated to dramatize what is at stake, well aware that the road to a successful presidency is full of stumbling blocks.
EU member states remain divided on the financial terms of enlargement, notably on subsidies to farmers in candidate countries.
Germany, the largest contributor to the EU budget, and the Netherlands do not want to pay out such subsidies until the EU reforms its costly common agricultural policy, which accounts for more than 40 percent of the EU's budget spending.
Complicating matters is the fact that Germany is to hold legislative elections in September, leaving other EU leaders wondering whether Chancellor Gerhard Schroeder will still be in power during an October mid-term summit in Brussels.
Besides enlargement, immigration is expected to be a major issue.
The EU summit in Madrid in June made a start on a common policy to curb illegal immigration which has caused increased concern in the bloc.
EU leaders agreed to crack down on illegal immigration, with the help of the poor nations from which immigrants flee, following the success of the far right in France and the Netherlands in exploiting the issue.
The conservative Danish government, which relies on the informal support of the right-wing Danish People's Party in Parliament, has already taken its own national measures to crack down on immigration, prompting concern among both the United Nations and other EU states.
Another hot issue during the presidency will be Ireland's referendum on the Nice Treaty, which voters there have already rejected once.
The Danish prime minister has warned that if Irish voters again reject the treaty at a second plebiscite due in October, the political framework for enlargement will crumble.
The Nice Treaty outlines the modus operandi of an enlarged EU, defining the distribution of European MPs between member states.
Faced with these challenges, Rasmussen has warned his colleagues, both in the EU member states and candidate countries, that they will have to be "flexible" over the next six months.
The Danish government has also made it clear that it plans to prioritize peace in the Middle East during its turn at the EU helm.
On June 30, Danish Foreign Minister Per Stig Moeller said he would unveil a peace plan for the region this week on behalf of the EU during an official visit to the United States.