Fredrik Reinfeldt, the Swedish prime minister, said there was "not a minute to lose" in talks to reach a deal at the global summit on reducing greenhouse gases to be held in Copenhagen in December.
Earlier this month, European leaders gave Jose Manuel Barroso, the commission president, only lukewarm support for his re-election for a second five-year term.
Meanwhile, the European parliament, which must also vote on the matter, has indicated it could postpone its decision until the autumn.
That would prolong the uncertainty and could give Barroso's critics on the left, the Greens and even the liberals, time to come up with a rival candidate.
The parliament is expected to announce on July 9 whether or not it will postpone its vote.
Reinfeldt has called for a rapid resolution to the issue, saying parliament should present an alternative candidate if it is not satisfied with Barroso.
Reinfeldt must also shepherd progress of the Lisbon Treaty, which is aimed at streamlining decision-making in the EU.
The treaty, which has to be ratified by all 27 EU members, is in limbo pending a new referendum that Ireland will hold in early October after Irish voters rejected it in a first plebiscite in June 2008.
Opinion polls suggest the "yes" side will win the referendum, but if those predictions are wrong Europe would be plunged into a new crisis.
If the treaty is ultimately ratified, Stockholm will then have to oversee the nominations, and wrangling between member states, for the new positions created in the treaty.
These include a de facto EU president and foreign minister who will enjoy wider powers.