That has not stopped Iran from trying. Mohammad-Reza Rahimi, Iran’s first vice president, arrived in Beirut a couple of weeks ago with at least a dozen proposals for Iranian-financed projects tucked under his arm, one for virtually every ministry, Lebanese officials said. The size of the Iranian delegation — more than 100 members — shocked government officials. Lebanese newspapers gleefully reported embarrassing details of the wooing; in their haste to repeat their success in forging closer ties with Iraq, for example, the Iranians forgot to replace the word Baghdad with Beirut in one draft agreement.

Iran offered to build the infrastructure needed to carry electricity across Iraq and Syria into Lebanon. It offered to underwrite Persian-language courses at Lebanon’s public university. Other proposals touched on trade, development, hospitals, roads, schools and, of course, the Balaa Dam in Tannourine.

Yet virtually no substantial new agreements were signed. The Iranian ambassador, Ghazanfar Roknabadi, reacted like a spurned suitor, grumbling publicly that Lebanon needed to do more to carry out agreements. The embassy here rejected a request for an interview, but Iran’s state-run Press TV quoted Mr. Roknabadi as saying, “The Iranian nation offers its achievements and progress to the oppressed and Muslim nations of the region.”

Therein lies the rub. Syria, run by a nominally Shiite Muslim sect, fostered its alliance with Iran as a counterweight to Sunni Muslim powers like Saudi Arabia. The alliance was built more on confronting the West and its allies than on any sectarian sympathies.

In Lebanon, a nation of various religious sects, many interpret Iran’s reference to “Muslim” as solely “Shiite Muslim.” Hezbollah insists that that is not the case and that the money comes with no strings attached and is for the good for all Lebanese.

“The Iranians say, ‘If you want factories, I am ready, if you want some electricity, I am ready,’ and they do not ask for any price in return,” said Hassan Jishi, the general manager of Waad, the organization that rebuilt the southern suburbs. (The name means “promise” in Arabic, referring to Mr. Nasrallah’s promise to reconstruct the area.) It cost $400 million to build apartments and stores for about 20,000 people, Mr. Jishi said.