The European Union has long called for unification of the fractious movement trying to topple President Bashar Assad, amid a conflict that has killed an estimated 38,000 people.
Foreign ministers will also discuss the exchange of attacks over the past week between Israel and militants in the Gaza Strip. But there is always a range of views within the European Union on Israel, diplomats said.
Israel has been giving off signs of a possible ground invasion of the Hamas-run enclave as the next stage in its air and sea offensive, which it says is aimed at stopping Palestinian rocket fire.
US President Barack Obama said that while Israel had a right to defend itself, it would be "preferable" to avoid an Israeli ground invasion.
In one diplomatic development in the Syrian conflict, France last week became the first European power to recognize the Syrian National Coalition as the sole representative of the Syrian people, and the French foreign minister later called for discussion of the possibility of supplying arms to the rebels.
But other Western states are holding back, uneasy over the presence of radical Islamists among the rebels and accusations by UN investigators of war crimes committed by rebel fighters.
British Foreign Secretary William Hague said on Friday that Britain needed first to know more about the group's plans.
A diplomat from another EU country said a unified opposition was an important political step, but cautioned: "We are going to assess the situation after the opposition has unified."
The bloc's 27 foreign ministers would try to reach conclusions that encourage the new coalition but stop short of giving it full recognition, another diplomat said.
However, the current EU arms embargo on Syria would not yet be lifted to help the opposition, diplomats said.
The new developments in the Middle East are a test for the EU foreign policy, which has run relatively smoothly when states have had time to hammer out common positions - ratcheting up sanctions against Iran and Syria this past year, for example.
But the European Union has struggled in the past to react quickly to breaking events, such as when Germany opposed military action during the popular uprising in Libya in 2011.
The EU foreign ministers will join defense ministers to discuss a plan to help train Malian forces to fight Islamists who have taken over the north of the country.
The European Union will likely send 200 troops to Mali to help training, plus security personnel to protect them, but Brussels has ruled out a combat role.
The ministers will also address Iran's nuclear program, after a UN report said Tehran was set to sharply expand its uranium enrichment in an underground plant.
The report showed that Iran's stockpile of its most sensitive nuclear material was getting closer to an amount that could be sufficient for a nuclear weapon.
EU foreign policy chief Catherine Ashton is scheduled to host a meeting of representatives of six powers in Brussels on Wednesday, as part of efforts to dissuade Iran from its nuclear program.
BRUSSELS (Reuters) -- EU foreign ministers will on Monday thrash out positions on increasingly thorny problems in the Middle East, but the bloc will likely not follow France in giving full recognition to the new Syrian opposition, diplomats said.