WASHINGTON—Mullah Abdul Ghani Baradar, the most senior Afghan Taliban leader in custody in Pakistan, is providing important information to American officials on the inner workings of the Taliban, pivotal insights as the United States looks ahead to negotiations to end the war in Afghanistan, according to senior American intelligence and military officials.

Baradar, the second-ranking Taliban leader, was arrested in January in Karachi, Pakistan, in an operation by American and Pakistani intelligence agents. His Pakistani captors initially limited American interrogators' access to him, but American officials say they have had regular, direct contact with Baradar for several weeks.

For now, officials say, Baradar is not revealing details of Taliban combat operations, yielding little that American commanders would like to know as they prepare for a military operation around Kandahar, the Taliban's spiritual base and Afghanistan's second-largest city.

But the officials said he had provided American interrogators with a much more nuanced understanding of the strategy that the Taliban's supreme leader, Mullah Muhammad Omar, is developing for negotiations with the government of President Hamid Karzai of Afghanistan, who is visiting Washington next week.

Baradar is describing in detail how members of the Afghan Taliban's leadership council, or shura, based in Pakistan, interact, and how senior members fit into the organization's broader leadership, officials said.

He is also offering a more detailed understanding of what prompted Omar to issue a new code of conduct for militants last year that directed fighters to avoid civilian casualties. American officials say the code was meant to project a softer image to the Afghan people.

“;He's provided very useful but not decisive information,”; an American counterterrorism official said on Wednesday.

Four American military, intelligence and diplomatic officials provided details of Baradar's cooperation, but requested anonymity because they were not authorized to speak publicly about the delicate intelligence interrogations.

Baradar, in his early 40s and said by most officials to belong to the same Popalzai tribe as Karzai, is believed to be one of a handful of Taliban leaders who were in periodic contact with Omar, the reclusive founder of the Taliban.

Baradar's capture was followed by arrests of two Taliban “;shadow governors”; in Pakistan. While the arrests showed a degree of cooperation between the Central Intelligence Agency and Pakistan's main spy agency, Inter-Services Intelligence, or ISI, they also illustrated how the Afghan Taliban leadership has relied on Pakistan as a rear base.

Even as American officials explain how Baradar's information could help defeat the insurgency in Afghanistan, they are nervously assessing Pakistan's ability not just to drive militants from South Waziristan and other contested areas, but also to hold that territory and build up civilian services and institutions.

“;Simply clearing these areas of the militants is insufficient,”; Lt. Gen. John Paxton, operations director for the Joint Chiefs of Staff, told the House Armed Services Committee last week. “;This progress would be undermined if the Pakistani security forces are unable to hold and gradually build in these areas.”;

Paxton said that American military liaisons in Pakistan had “;recently noted the trickling in and the return of militants in previously cleared areas.”;

Many questions remain about Baradar's capture and Pakistan's motivations. It appears, for instance, that Pakistani authorities did not realize at first their captive's significance. But they have tried to turn his arrest to their advantage and are poised to use him as a chip in bargaining between the Afghan government and the Taliban and, conceivably, even as a negotiator.

“;The key issue is we should decide jointly how we are going to benefit from his presence,”; a senior Pakistani intelligence official in Islamabad said recently.

Initially, some American military officials said that taking Baradar off the battlefield, and exploiting information he might provide, could deal a blow to Taliban military capacity.

But Omar has replaced Baradar, his top deputy, with Mullah Abdul Qayyum Zakir, a former detainee at Guantanamo Bay, Cuba, who is believed to be in his mid-30s and has a reputation as a tough fighter with few political skills.

And senior Taliban officials have sought to discount the impact of Baradar's detention on their bargaining position.

“;The Taliban would be ready to negotiate but under our own conditions,”; a member of the Afghan Taliban's supreme command said in an interview. “;To assume that they would hold the Taliban leadership hostage because of Mullah Baradar's arrest is not something that would cross our mind.”;