Americans fighting the war in Afghanistan have long harbored strong suspicions that Pakistan’s military spy service has guided the Afghan insurgency with a hidden hand, even as Pakistan receives more than $1 billion a year from Washington for its help combating the militants, according to a trove of secret military field reports made public Sunday.

The documents, made available by an organization called WikiLeaks, suggest that Pakistan, an ostensible ally of the United States, allows representatives of its spy service to meet directly with the Taliban in secret strategy sessions to organize networks of militant groups that fight against American soldiers in Afghanistan, and even hatch plots to assassinate Afghan leaders.

Taken together, the reports indicate that American soldiers on the ground are inundated with accounts of a network of Pakistani assets and collaborators that runs from the Pakistani tribal belt along the Afghan border, through southern Afghanistan, and all the way to the capital, Kabul.

Much of the information — raw intelligence and threat assessments gathered from the field in Afghanistan— cannot be verified and likely comes from sources aligned with Afghan intelligence, which considers Pakistan an enemy, and paid informants. Some describe plots for attacks that do not appear to have taken place.

But many of the reports rely on sources that the military rated as reliable.

While current and former American officials interviewed could not corroborate individual reports, they said that the portrait of the spy agency’s collaboration with the Afghan insurgency was broadly consistent with other classified intelligence.

Some of the reports describe Pakistani intelligence working alongside Al Qaeda to plan attacks. Experts cautioned that although Pakistan’s militant groups and Al Qaeda work together, directly linking the Pakistani spy agency, the Directorate for Inter-Services Intelligence, or ISI, with Al Qaeda is difficult.

The records also contain firsthand accounts of American anger at Pakistan’s unwillingness to confront insurgents who launched attacks near Pakistani border posts, moved openly by the truckload across the frontier, and retreated to Pakistani territory for safety.

The behind-the-scenes frustrations of soldiers on the ground and glimpses of what appear to be Pakistani skullduggery contrast sharply with the frequently rosy public pronouncements of Pakistan as an ally by American officials, looking to sustain a drone campaign over parts of Pakistani territory to strike at Qaeda havens. Administration officials also want to keep nuclear-armed Pakistan on their side to safeguard NATO supplies flowing on routes that cross Pakistan to Afghanistan.

This month, Secretary of State Hillary Rodham Clinton, in one of the frequent visits by American officials to Islamabad, announced $500 million in assistance and called the United States and Pakistan “partners joined in common cause.”

The reports suggest, however, that the Pakistani military has acted as both ally and enemy, as its spy agency runs what American officials have long suspected is a double game — appeasing certain American demands for cooperation while angling to exert influence in Afghanistan through many of the same insurgent networks that the Americans are fighting to eliminate.

Behind the scenes, both Bush and Obama administration officials as well as top American commanders have confronted top Pakistani military officers with accusations of ISI complicity in attacks in Afghanistan, and even presented top Pakistani officials with lists of ISI and military operatives believed to be working with militants.

Benjamin Rhodes, deputy national security adviser for strategic communications, said that Pakistan had been an important ally in the battle against militant groups, and that Pakistani soldiers and intelligence officials had worked alongside the United States to capture or kill Qaeda and Taliban leaders.

Still, he said that the “status quo is not acceptable,” and that the havens for militants in Pakistan “pose an intolerable threat” that Pakistan must do more to address.

“The Pakistani government — and Pakistan’s military and intelligence services — must continue their strategic shift against violent extremist groups within their borders,” he said. American military support to Pakistan would continue, he said.

Several Congressional officials said that despite repeated requests over the years for information about Pakistani support for militant groups, they usually receive vague and inconclusive briefings from the Pentagon and C.I.A.

Nonetheless, senior lawmakers say they have no doubt that Pakistan is aiding insurgent groups. “The burden of proof is on the government of Pakistan and the ISI to show they don’t have ongoing contacts,” said Senator Jack Reed, a Rhode Island Democrat on the Armed Services Committee who visited Pakistan this month and said he and Senator Carl Levin of Michigan, the committee chairman, confronted Pakistan’s prime minister, Yousaf Raza Gilani, yet again over the allegations.

Such accusations are usually met with angry denials, particularly by the Pakistani military, which insists that the ISI severed its remaining ties to the groups years ago. An ISI spokesman in Islamabad said Sunday that the agency would have no comment until it saw the documents. Pakistan’s ambassador to the United States, Husain Haqqani, said, “The documents circulated by WikiLeaks do not reflect the current on-ground realities.”

The man the United States has depended on for cooperation in fighting the militants and who holds most power in Pakistan, the head of the army, Gen. Parvez Ashfaq Kayani, ran the ISI from 2004 to 2007, a period from which many of the reports are drawn. American officials have frequently praised General Kayani for what they say are his efforts to purge the military of officers with ties to militants.

American officials have described Pakistan’s spy service as a rigidly hierarchical organization that has little tolerance for “rogue” activity. But Pakistani military officials give the spy service’s “S Wing” — which runs external operations against the Afghan government and India — broad autonomy, a buffer that allows top military officials deniability.

American officials have rarely uncovered definitive evidence of direct ISI involvement in a major attack. But in July 2008, the C.I.A.’s deputy director, Stephen R. Kappes, confronted Pakistani officials with evidence that the ISI helped plan the deadly suicide bombing of India’s Embassy in Kabul.

From the current trove, one report shows that Polish intelligence warned of a complex attack against the Indian Embassy a week before that bombing, though the attackers and their methods differed. The ISI was not named in the report warning of the attack.

Another, dated August 2008, identifies a colonel in the ISI plotting with a Taliban official to assassinate President Hamid Karzai. The report says there was no information about how or when this would be carried out. The account could not be verified.

General Linked to Militants

Lt. Gen. Hamid Gul ran the ISI from 1987 to 1989, a time when Pakistani spies and the C.I.A. joined forces to run guns and money to Afghan militias who were battling Soviet troops in Afghanistan. After the fighting stopped, he maintained his contacts with the former mujahedeen, who would eventually transform themselves into the Taliban.

And more than two decades later, it appears that General Gul is still at work. The documents indicate that he has worked tirelessly to reactivate his old networks, employing familiar allies like Jaluluddin Haqqani and Gulbuddin Hekmatyar, whose networks of thousands of fighters are responsible for waves of violence in Afghanistan.

General Gul is mentioned so many times in the reports, if they are to be believed, that it seems unlikely that Pakistan’s current military and intelligence officials could not know of at least some of his wide-ranging activities.

For example, one intelligence report describes him meeting with a group of militants in Wana, the capital of South Waziristan, in January 2009. There, he met with three senior Afghan insurgent commanders and three “older” Arab men, presumably representatives of Al Qaeda, who the report suggests were important “because they had a large security contingent with them.”

The gathering was designed to hatch a plan to avenge the death of “Zamarai,” the nom de guerre of Osama al-Kini, who had been killed days earlier by a C.I.A. drone attack. Mr. Kini had directed Qaeda operations in Pakistan and had spearheaded some of the group’s most devastating attacks.

The plot hatched in Wana that day, according to the report, involved driving a dark blue Mazda truck rigged with explosives from South Waziristan to Afghanistan’s Paktika Province, a route well known to be used by the insurgents to move weapons, suicide bombers and fighters from Pakistan.

In a show of strength, the Taliban leaders approved a plan to send 50 Arab and 50 Waziri fighters to Ghazni Province in Afghanistan, the report said.

General Gul urged the Taliban commanders to focus their operations inside Afghanistan in exchange for Pakistan turning “a blind eye” to their presence in Pakistan’s tribal areas. It was unclear whether the attack was ever executed.