BEIRUT, Lebanon — President Bashar al-Assad of Syria said Monday that a United Nations proposal for a local cease-fire in Syria’s largest city, Aleppo, was worth considering. It was Mr. Assad’s first response to the idea floated recently by the new United Nations envoy to Syria.

The envoy, Staffan de Mistura, has suggested “freezing” the conflict in Aleppo as a way of calming the Syrian conflict, aiding the fight against the extremist Islamic State militant group and advancing what has so far been a fruitless quest for a political solution.

The modesty of the Aleppo proposal — halting the fighting in just one corner of a chaotic battlefield — reflects how the United Nations has scaled back its goals and expectations after more than three years of a conflict that has killed more than 150,000 people, displaced 6.5 million people inside Syria and driven more than three million others from the country.