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

Although the offer made by the opposition leader, Sheik Ahmad Moaz 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. While some complained that Sheik Khatib had not consulted them before making the offer and a few even called for his resignation, others went along in part to counter the appearance of fractiousness that has long been a weakness in the opposition.

Sheik Khatib, a respected Sunni cleric in exile who once was the head imam at the historic Umayyad Mosque in Damascus, said he would engage in dialogue with Mr. Assad’s government only if it released 160,000 political prisoners and renewed all expired passports held by members of the Syrian diaspora, which includes large numbers of dissidents.

On Sunday, an aide to Mr. Assad gave a vague response. The aide, Ali Haidar, Syria’s minister of national reconciliation, said in an interview with Russia Today, a Kremlin-financed news organization sympathetic to Syria’s government, that the government was open to talks with any opposition members who reject violence. He also said it was willing to address the passport issue, but not necessarily the release of prisoners. Mr. Haidar said the 160,000 figure was exaggerated and asked Sheik Khatib to send a list of prisoner names.