DAMASCUS, Syria — As Islamists increasingly fill the ranks of Syrian rebels, President Bashar al-Assad is waging an energized campaign to persuade the United States that it is on the wrong side of the civil war. Some government supporters and officials believe they are already coaxing — or at least frightening — the West into holding back stronger support for the opposition.

Confident they can sell their message, government officials have eased their reluctance to allow foreign reporters into Syria, paraded prisoners they described as extremist fighters and relied unofficially on a Syrian-American businessman to help tap into American fears of groups like Al Qaeda.

“We are partners in fighting terrorism,” Syria’s prime minister, Wael Nader al-Halqi, said.

Omran al-Zoubi, the information minister, said: “It’s a war for civilization, identity and culture. Syria, if you want, is the last real secular state in the Arab world.”

Despite hopes in Damascus, President Obama has not backed off his demand that Mr. Assad step down. The administration has also kept up economic pressure on his government and has increased nonlethal aid to the opposition while calling for a negotiated settlement to the fighting.