BEIRUT — Syria’s opposition coalition gave qualified backing Monday to its leader’s surprise offer last week for a dialogue with President Bashar Assad to end the civil war, pressing him to respond definitively and even suggesting he could avoid trial if he resigned and left the country.

Although the offer made by the opposition leader, Mouaz al-Khatib, was by his own admission a personal gambit and was initially greeted with a torrent of criticism inside the Syrian opposition movement, his colleagues in the National Coalition of Syrian Revolutionary and Opposition Forces basically endorsed it over the weekend.