CHICAGO - David Coleman Headley, the former Philadelphian who is the government's key witness in the trial of a Chicago businessman accused of helping coordinate the 2008 Mumbai terror attacks, described Monday how he made multiple scouting trips to India before the rampage and gave frequent updates about his progress to his two Pakistani handlers: one from an anti-India group, and the other from the country's main intelligence agency.

The federal trial of businessman Tahawwur Rana is being closely watched around the world for what Headley, Rana's longtime friend, might reveal about possible links between the extremist group, Lashkar-e-Taiba, and Pakistan's Inter-Services Intelligence agency.

Headley pleaded guilty last year to scouting targets for the Mumbai attacks, and he agreed to testify against Rana to avoid the death penalty, making him one of the most valuable U.S. government counterterrorism witnesses.

What Headley - a Pakistani American whose mother was a Main Line socialite - says on the witness stand has the potential to inflame tensions between Pakistan and India and add pressure to the frayed U.S.-Pakistani relationship.

His testimony also could add to questions about Pakistan's commitment to catch terrorists and about the ISI's connections to Pakistan-based extremist groups, especially after Osama bin Laden was killed by U.S. forces in a military garrison town outside Islamabad earlier this month.

The Pakistani government has denied that the ISI orchestrated the three-day siege in Mumbai that killed 164 people, including six Americans. Pakistani intelligence officials have not commented on the trial.

"Headley's testimony is a nail in the coffin of U.S.-Pakistani strategic cooperation," said Bruce Riedel, a former White House adviser on Middle Eastern and South Asian issues.

After opening statements Monday at Rana's trial, the government called Headley to the stand, where he spent hours detailing the formulation of the attacks and Rana's alleged help in providing cover for Headley's surveillance activities in India.

Headley, clean-shaven and balding, wore a light-blue golf shirt with a dark windbreaker. Speaking so softly at times that attorneys had to remind him to speak louder, Headley said he had been involved with Lashkar for more than a decade, but wasn't working with someone in the ISI until years later, after his arrest by tribal police near Afghanistan. It was then, he said, that he met a major in the ISI and told the major what he and Lashkar were planning.

The major, Headley said, was "very pleased" with what he heard and asked if Headley would work with one of his ISI associates. Headley agreed and said he was released from custody. Headley soon received a call from a man he referred to during his testimony as "Major Iqbal," which the U.S. government says is an alias. Headley said he met Iqbal in a safe house in Lahore, Pakistan, and described his plans with Lashkar and his assignment to take videos of Mumbai in preparation for an operation.

Headley said that the ISI provided financial and military assistance to Lashkar, and that he assumed they worked under the same umbrella.

He said that Iqbal and his Lashkar handler, Sajid Mir, were in communication but that he would meet with them separately in Pakistan. Headley said that when he would take videos of sights in Mumbai, he would first share them with Iqbal and then with Mir.

"They coordinated with each other, and ISI provided assistance to Lashkar," Headley told jurors.

Before moving to Mumbai in late 2006, Headley said, he first came to Chicago, met with Rana, and explained the plot in hopes of persuading Rana to let Headley open a branch of Rana's immigration-services business as a cover.

"I knew my friend had an office and I could persuade him to help us out," Headley testified.

With Rana's help, Headley said, he set up an immigration-consulting business in Mumbai and secured work visas to travel in and out of India. Headley described conversations he had with Rana while he was visiting in Chicago, and prosecutors showed e-mail messages between the two men discussing the immigration business and Mumbai operation through coded words.

Headley said he first told Rana about his involvement with Lashkar in August 2005. Headley said his friend was surprised to learn this, but did not say he disapproved.

Earlier Monday, attorneys painted opposing portraits of Rana, a Pakistani-born Canadian who has lived in Chicago for years.

Assistant U.S. Attorney Sarah Streicker told jurors, "The defendant knew all too well that when Headley travels to a foreign country, people may die."

Defense attorney Charles Swift described Headley as a man who had manipulated people for years, including Rana. Swift said Headley had a history of cooperating with the government to get out of trouble, and he spoke of Headley's work with the Drug Enforcement Administration in the 1990s. At one point, Swift said, Headley was working simultaneously for the DEA, Lashkar and Pakistani intelligence.

Rana, 50, has pleaded not guilty in the case. His name is the seventh one on the federal indictment, and he is the only defendant in custody. Among the six others charged in absentia are Mir and Iqbal.

Headley's testimony is expected to resume Tuesday.