Mr Barroso has said the EU will back short-term measures to address social hardship, but he has warned that high oil prices have to be tackled with long-term plans.
Our correspondent says the summit will reassure Balkan countries that they can join the bloc when they meet the required economic and political conditions, and back plans for an "eastern partnership" with former Soviet republics like Ukraine.
The President of the European Parliament, Hans-Gert Poettering, insisted that accession negotiations with Croatia and Turkey would continue despite the Lisbon Treaty ratification problem.
"No-one thinks the negotiations with Turkey will be halted," he told reporters in Brussels.
But diplomats say it will be difficult to continue with enlargement until the EU can agree on ways to work better, either with or without the reform treaty.
Germany and France have been at pains to impress this on the Czech Republic and Poland, which are keen on eastward expansion of the EU but hesitating over ratification of Lisbon.
At the summit, the leaders will also turn their attention to Zimbabwe's forthcoming elections.
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