Mr. Saleh fled the country last week to seek medical treatment in Saudi Arabia after rebel shelling of the presidential compound, and more government troops have been brought back to Sana to bolster the government’s defense.

“We’ve seen the regime move its assets away from counterterrorism and toward its own survival,” said Christopher Boucek, a Yemen expert at the Carnegie Endowment for International Peace. “But as things get more and more chaotic in Yemen, the space for the Americans to operate in gets bigger,” he said.

But Mr. Boucek and others warned of a backlash from the American airstrikes, which over the past two years have killed civilians and Yemeni government officials. The benefits of killing one or two Qaeda-linked militants, he said, could be entirely eroded if airstrikes kill civilians and lead dozens of others to jihad.

Edmund J. Hull, ambassador to Yemen from 2001 to 2004 and the author of “High-Value Target: Countering Al Qaeda in Yemen,” called airstrikes a “necessary tool” but said that the United States had to “avoid collateral casualties or we will turn the tribes against us.”

Al Qaeda’s affiliate in Yemen is believed by the C.I.A. to pose the greatest immediate threat to the United States, more so than even Qaeda’s senior leadership believed to be hiding in Pakistan. The Yemen group has been linked to the attempt to blow up a transatlantic jetliner on Christmas Day 2009 and last year’s plot to blow up cargo planes with bombs hidden inside printer cartridges.

Mr. Harithi, the militant killed on Friday, was an important operational figure in Al Qaeda in the Arabian Peninsula and was believed to be one of those responsible for the group’s ascendance in recent years. According to people in Yemen close to the militant group, Mr. Harithi travelled to Iraq in 2003 and fought alongside Abu Musab al-Zarqawi, the Jordanian operative who led the Qaeda affiliate in Iraq until he was killed in an American strike in 2006. Mr. Harithi returned to Yemen in 2004, those close to the militants said, where he was captured, tried and imprisoned in 2006 but released three years later.

Even as senior administration officials worked behind the scenes with Saudi Arabia for a transitional government to take power in Yemen, a State Department spokesman on Wednesday called on the embattled government in Sana to remain focused on dealing with the rebellion and Qaeda militants.

“With Saleh’s departure for Saudi Arabia, where he continues to receive medical treatment, this isn’t a time for inaction,” said the spokesman, Mark Toner. “There is a government that remains in place there, and they need to seize the moment and move forward.”