Francois Hollande and David Cameron are likely to urge other EU leaders to lift an arms embargo on Syria which prohibits the supply of weapons to rebels fighting Bashar al-Assad.
The French president and British prime minister are in Brussels for the EU summit, which also coincides with the second anniversary of the start of the Syrian uprising against Assad's regime.
"We want Europeans to lift the arms embargo. Britain and France agree on this option," said Hollande ahead of the two-day summit.
Reports suggest Cameron held separate talks with Hollande over the situation in Syria before the summit.
Hollande told reporters: "We are ready to support the rebellion, so we are ready to go this far. We must take our responsibilities."
The two-year unrest began on 15 March 2011. Since then it claimed 70,000 lives and forced a million people to flee the country as refugees.
Although the lightly-armed opposition groups have taken control large portions of the country, the stalemate with the heavily-armed Assad regime continues.
"We cannot allow the massacre of a people by a regime which right now does not want a political transition. France's view is that arms are being delivered to Syria - but to the regime of Bashar, in particular by the Russians," said Hollande, insisting that the aim of proposal is not a "total war."
German Chancellor Angela Merkel said, "If our partners in the European Union, in this case Britain and France, have a changed assessment of the situation, then the foreign ministers are of course ready to discuss this subject again."
Russia, Assad's key ally, strongly opposes to the move of supplying the rebels with weapons. Russian Foreign Minister Sergei Lavrov reiterated Moscow's position saying that "arming the opposition is not an option."
The proposal has been welcomed by the anti-Assad groups and enraged Damascus.
Anti-regime forces have asked for heavy weapons in order to balance the ongoing battle against Assad. However, many European leaders stand opposed to the move fearing that it would escalate the civil war further.
Washington has made it clear that that the US looks forward to see "many governments" to provide "appropriate support" to the Syrian rebels.
The EU embargo was extended for three months on 28 February by the EU foreign ministers.