"After an introductory round of consultations with his fellow heads of state and government, Swedish Prime Minister Fredrik Reinfeldt has decided to convene an extra informal summit on 19 November," the EU presidency said in a statement.
It is hoped that the 27 European heads of state and government will reach agreement at the dinner summit on the key new posts created by the EU's reforming Lisbon Treaty, ratified this month.
"My prime minister is going to start a second round of consultations and hopefully we will be able to present the candidates next Thursday," Roberta Alenius, spokeswoman for Reinfeldt told AFP in Stockholm.
However, filling the two posts is proving more difficult than many had expected.
The Swedes wound up a first round of talks with no consensus for either post and many names swirling around, the spokeswoman said.
The British government still backs former premier Tony Blair, despite unpopularity in some European quarters over his support for the war in Iraq.
Others see Britain as on the periphery of the European project as it has joined neither the euro currency nor the passport-free Schengen area.
Current British Prime Minister Gordon Brown said on Tuesday that his foreign secretary David Miliband "was never a candidate" for the foreign affairs post.
British Business Secretary Peter Mandelson, a former EU commissioner, said he had been sounded out for the job left open by Miliband.
The current favourite to become president of the EU council is Belgium's centre-right Prime Minister Herman Van Rompuy, who has French and German support according to diplomats.
However the discreet negotiator, busy keeping feuding Dutch-speaking Flemish and the francophone parties together in his national coalition government, could find himself overshadowed by his main backers and, if chosen, find his role reduced to facilitator and consensus builder.
That could leave the way clear for a more forceful foreign policy chief, taking a firm platform to the likes of the China, Russia and the United States.
Reinfeldt, in a Swedish press interview on Wednesday, underlined the difficulties involved in choosing the two key diplomats.
"My discussions show how important it is to have a good balance in the choice of posts," he told the daily Dagens Nyheter.
"The balance between left and right is very important for many, but also between big and small nations, between north and south, men and women," said Reinfeldt.
"It's difficult to fill all the criteria," he added.
Many European countries, including France, hope to seal a deal this week.
In theory the Lisbon Treaty would allow the president's post to be agreed via a qualified majority of EU member states. In practice everyone wants a unanimous decision.
Reinfeldt, who has found it hard to hide his frustration at Franco-German pressure, according to media reports, told the London Times that he might have to resort to the majority option.
He said qualified candidates for the EU president's post would essentially be former or current prime ministers.
The Swedish leader also faces a demand from Poland that shortlisted candidates undergo interviews.
Other names mentioned for the president's post have included Dutch Prime Minister Peter Balkenende and former Latvian president Vaira Vike-Freiberga.
For the foreign affairs post, former Italian prime minister Massimo D'Alema is being talked about as a strong candidate in the event of Miliband's regularly stated unavailability.
Sweden has led the discussions since Czech President Vaclav Klaus formally ratified the Lisbon treaty on November 3.