WASHINGTON — The United States is laying the groundwork for operations to kill or capture militants implicated in the deadly attack on a diplomatic mission in Libya, senior military and counterterrorism officials said Tuesday, as the weak Libyan government appears unable to arrest or even question fighters involved in the assault.

The top-secret Joint Special Operations Command is compiling so-called target packages of detailed information about the suspects, the officials said. Working with the Pentagon and the CIA, the command is preparing the dossiers as the first step in anticipation of possible orders from President Obama to take action against those determined to have played a role in the attack on a diplomatic mission in the eastern city of Benghazi that killed Ambassador J. Christopher Stevens and three colleagues three weeks ago.

Potential military options could include drone strikes, Special Operations raids such as the one that killed Osama bin Laden, and joint missions with Libyan authorities. But administration officials say no decisions have been made on any potential targets.

Spokesmen for the Defense Department and CIA declined to comment.

The preparations underscore the bind confronting the White House over the Benghazi attack. Obama has vowed to bring the killers to justice, and in the final weeks of the presidential campaign Republicans have hammered the administration over the possible intelligence failures that preceded the attack — including a new accusation that repeated requests for strengthened security in Benghazi had been rejected.

But any US military action on Libyan soil would risk casualties and almost certainly set off a popular backlash at a moment when gratitude for US support in the revolution that toppled Moammar Khadafy a year ago has created a measure of appreciation for the United States in the region.

At the same time, the Libyan government has presented a further issue by opposing any unilateral US military action in Libya to apprehend the attackers.  

“We will not accept anyone entering inside Libya,’’ Mustafa Abu Shagur, Libya’s prime minister, told the Al-Jazeera television network. ‘‘That would infringe on sovereignty and we will refuse.’’

The Libyan government still depends on autonomous local militias to act as the police, complicating any effort to detain the most obvious suspects. Libyan and US officials acknowledge the possibility that some of the perpetrators may have fled the country.

‘‘It is a kind of hypocrisy really,’’ said Fathi Baja, a liberal former member of the Transitional National Council from Benghazi, noting that despite promises of swift retribution, the government has not taken any steps to confront or interrogate those most widely believed to bear responsibility.

Both US counterterrorism officials and Benghazi residents are increasingly focused on the local militant group Ansar al-Shariah as the main force behind the attack. Counterterrorism officials in Washington say they now believe that Ansar al-Shariah had a rough attack plan for the US diplomatic mission ‘‘on the shelf’’ and ready for some time just in case.

Then, a US official said, reports of the breach of the US Embassy in Cairo, on the 11th anniversary of the Sept. 11, 2001, terrorist attacks against the United States, provided the impetus to put the Benghazi attack in motion.

In the hours after the Benghazi attack, the US official said, spy agencies intercepted electronic communications from Ansar al-Shariah fighters bragging to an operative with Al Qaeda in the Islamic Maghreb, an Algerian insurgency that has made itself a namesake of the global terrorist group founded by Osama bin Laden.