The CIA has relied on Lilley, part of a constellation of agency bases across Afghanistan, as a hub to train and deploy a well-armed 3,000-member Afghan paramilitary force collectively known as Counterterrorism Pursuit Teams. In addition to being used for surveillance, raids and combat operations in Afghanistan, the teams are crucial to the United States' secret war in Pakistan, according to current and former U.S. officials.

The existence of the teams is disclosed in "Obama's Wars," a forthcoming book by longtime Washington Post journalist Bob Woodward. But, more broadly, interviews with sources familiar with the CIA's operations, as well as a review of the database of 76,000 classified U.S. military field reports posted last month by the Web site WikiLeaks, reveal an agency that has a significantly larger covert paramilitary presence in Afghanistan and Pakistan than previously known.

The operations are particularly sensitive in Pakistan, a refuge for senior Taliban and al-Qaeda leaders where U.S. units are officially prohibited from conducting missions.

The WikiLeaks reports, which cover the escalation of the Afghan insurgency from 2004 until the end of 2009, include many descriptions of the activities of the "OGA" and "Afghan OGA" forces. OGA, which stands for "other government agency," is generally used as a reference to the CIA.

In clipped and coded language, the field logs provide glimpses into the kinds of operations undertaken by the CIA and its Afghan paramilitary units along the Pakistani border. In addition to accounts of snatch-and-grab operations targeting insurgent leaders, the logs contain casualtyreports from battles with the Taliban, summaries of electronic intercepts of enemy communications and hints of the heavy firepower at the CIA's disposal.

The CIA declined to comment on the Counterterrorism Pursuit Teams. A Pakistani official said the government will not comment on Woodward's book until after it is released.

A U.S. official familiar with the operations, speaking on the condition of anonymity, described the teams as "one of the best Afghan fighting forces," adding that they have made "major contributions to stability and security."

The official said that the teams' primary mission is to improve security in Afghanistan and that they do not engage in "lethal action" when crossing into Pakistan. Their cross-border missions are "designed exclusively for intelligence collection," the official said.

In addition to Firebase Lilley, in Paktika province, the WikiLeaks logs reveal the existence of an "OGA compound"at Forward Operating Base Orgun-E, another U.S. military installation in Paktika.

The field reports show that casualties are common for Afghan paramilitary forces training and operating there.

On Oct. 6, 2009, for example, an "OGA-trained" fighter was ambushed near Orgun-E while off duty, according to one log; he was treated on the base for gunshot wounds to the face, lower leg and hand.

The logs also indicate that the CIA and its Afghan units are at times involved in heavy fighting, in contrast to long-standing perceptions that the agency has largely served to direct attacks carried out by U.S. Special Operations forces or conventional military units.

On Aug. 11, 2008, U.S. soldiers stationed at Firebase Lilley reported that insurgents were targeting the base with rocket fire, a common occurrence. The soldiers responded at first with counterfire but then paused because of the "OGA dropping bombs," including three 500-pound explosives, according to an Army field report. The counterattack apparently worked, as no casualties were reported.

According to the logs, CIA forces also have mortars in their arsenal. On at least one occasion, in March 2008, the CIA used 81-millimeter rockets to repel an attack on Forward Operating Base Chapman, the same compound that a Jordanian suicide bomber later targeted in Dec. 30, 2009, killing seven CIA operatives. Chapman is in Khost province, also near the Pakistani border.

The agency's paramilitary wing, known as the Special Activities Division, has been active in Afghanistan since the U.S.-backed effort to oust the Taliban government began in 2001. But current and former U.S. intelligence officials said that the CIA almost immediately began assembling an elite Afghan commando force that has expanded in scale and mission over the past nine years.

A former senior CIA official involved in the formation of the Counterterrorism Pursuit Teams said the first unit was created in Kabul shortly after the U.S.-backed invasion in 2001. The team based in the capital remains the largest and most sophisticated, and it is routinely used to carry out operations elsewhere in the country, the former official said.

Over the past eight years, however, new units have been created in other locations, including Kandahar. Their missions vary from sensitive intelligence-gathering operations to carefully orchestrated takedowns of Taliban targets.

When intelligence indicates a Taliban or al-Qaeda presence in a nearby village, the teams often make the first move. "You might knock on the door. You might ask a neighbor. Or you might raid the place," the former official said.

Most of the teams are trained in Afghanistan by CIA and U.S. Special Operations forces. "Unlike the Afghan army, these guys are fairly well paid, very well motivated," the former official said.

The Army field reports suggest that the Afghan paramilitary forces can also be ruthless. On Oct. 23, 2007, military personnel at Orgun-E reported treating a 30-year-old Afghan man for the "traumatic amputation of fingers" on his left hand. The patient had been "injured by Afghan OGA during a home breach," according to the report.

The CIA has been running operations for several years from its eastern Afghan bases, which generally are shared with U.S. Special Operations forces and other military units. U.S. officials said that the CIA and the military frequently use different names for the same base and that the agency code names do not necessarily correspond with those used in the WikiLeaks records.

In October 2003, two Americans working on contract for the CIA were killed near a U.S. military outpost in the Shkin Valley in Paktika province. The outpost, then known as Firebase Shkin, was renamed in 2007 to honor Master Sgt. Arthur L. Lilley, a U.S. Special Forces soldier who was killed in a firefight there.

The CIA has also used the border bases to build and manage networks of ethnic Pashtun informants who cross into Pakistan's tribal belt. In combination with near-constant surveillance from U.S. drone aircraft in the skies, the informants have enabled the CIA to identify the whereabouts of al-Qaeda and Taliban leaders.

That has led to an exponential increase in missile attacks by the drones. The CIA has carried out 71 drone strikes in Pakistani territory this year, more than double the number for all of 2008, according to statistics compiled by the New America Foundation.

At the same time, the border-hugging bases have reduced the CIA's dependence on Pakistan's Inter-Services Intelligence directorate, a mercurial spy service that has helped track down dozens of al-Qaeda and other insurgent leaders but is also considered a secret supporter of the Afghan Taliban.

For years, the ISI restricted CIA operatives to Pakistani bases in the tribal belt and strictly controlled access to its sources in the region. As a result, the Americans were kept largely in the dark about the presence of al-Qaeda and Taliban forces on that side of the border.

whitlockc@washpost.com millergreg@washpost.com

Staff researcher Julie Tate contributed to this report.