Though Hezbollah’s base in Lebanon remains strong, it runs an increasing risk of finding itself isolated, possibly caught up in a sectarian war between its patron, Iran, the region’s Shiite power, and Saudi Arabia, a protector of Sunni interests in the Middle East. Its longtime ally, Hamas, the Palestinian militant group, has distanced itself from the Assad government, moving its headquarters out of Damascus, and Sunni revolutionaries in Syria have explicitly denounced Hezbollah as an enemy. At home, its Lebanese rivals sense a rare opportunity to erode its power.

In a delicate adjustment in the face of these new realities — and the resilience of the uprising — Hezbollah has shifted its tone. In carefully calibrated speeches last month, Mr. Nasrallah gently but firmly signaled that Mr. Assad could not crush the uprising by force and must lay down arms and seek a political settlement. He implicitly acknowledged the growing moral outrage in the wider Muslim world at the mounting death toll, obliquely noted that the Syrian government was accused of “targeting civilians” and urged Mr. Assad to “present the facts to the people.”

Behind the scenes, Mr. Nasrallah personally tried to start a reconciliation process in Syria early in the uprising and is now renewing those efforts, said Ali Barakeh, a Hamas official involved in the talks.

“He refuses the killing for both sides,” said Mr. Barakeh, the Beirut representative for Hamas.

Mr. Barakeh said that Mr. Nasrallah visited Damascus in April of last year and briefly persuaded Mr. Assad to try to reach a political solution, with Hezbollah and Hamas acting as mediators. But as Hamas began reaching out to fellow Sunni Muslims in the opposition, the plan was scuttled by the Syrian government.

Hezbollah rarely allows official interviews and has refused them for months. But supporters and current and former party activists suggest that the situation is fueling fears of an anti-Shiite backlash and is testing loyalists who must explain the party’s position to others, and themselves.