At the start of a federal trial in Manhattan that may shed light on the inner workings of Afghanistan’s drug trade, prosecutors are painting the picture of a warlord who used his clout with the Taliban to smuggle heroin into America.

Bashir Noorzai, a tribal leader-cum-Taliban associate-cum-American informant, was arrested on drug charges in 2005 after he provided federal agents with potentially valuable information on a wanted terrorist. To hear prosecutors tell it, Mr. Noorzai tried to woo the Americans in a selfish bid to restore his power in Afghanistan. The defense, meanwhile, is portraying a man who offered to help America secure the country and catch a dangerous enemy, and who received a pair of handcuffs as thanks for his trouble.

The contrasting accounts yesterday kicked off a battle to profile Mr. Noorzai, the leader of a tribe of about 1 million people in southern Afghanistan. He is charged with producing heroin there and sending $50 million worth of it into America.

A federal prosecutor described how Mr. Noorzai used drug profits to help the Taliban gain control of southern Afghanistan in the 1990s. He then “exploited his influence with the Taliban to continue his drug trafficking with impunity,” the attorney, Anirudh Bansal, said.

Later, after the American invasion, Mr. Noorzai agreed to meet with federal agents at the Embassy Suites Hotel in Manhattan. Over the course of an 11-day interview, he offered potentially critical information about how American troops could track down the leader of the Taliban, Mullah Mohammad Omar, who remains at large today.

“He hoped that he could help himself by offering to help the U.S. government,” Mr. Bansal said.

The prosecution said he also confessed details about his role in trafficking opium and heroin. Mr. Noorzai was arrested on drug charges at the conclusion of the meeting, despite what he claims were government assurances that he would enjoy safe passage in America.

His lawyer, Ivan Fisher, said Mr. Noorzai had traveled to New York because he made a decision — “an apparently foolish decision” — to help America secure Afghanistan using his power base there.

“This wasn’t a confession,” Mr. Fisher said. “This was a proposal.”

The testimony slated for this trial may offer some new insight into Afghanistan’s rampant drug trade, which provides about 90% of the world’s heroin and has helped finance the Taliban’s revival. The prosecution plans to put several of Mr. Noorzai’s alleged associates on the stand.

Mr. Fisher began to chip away at the credibility of those witnesses yesterday. One of them is Baz Mohammad, who claimed to have waged “jihad” against America through drug trafficking, according to Mr. Fisher.

Mr. Noorzai suffered a major defeat last month, when a judge ruled that he could stand trial even if he was deceived into coming to New York. The meeting with federal agents had been arranged by a security company, Rosetta Research and Consulting LLC, which during its brief existence sought to help governments conduct investigations in other countries. Mr. Noorzai claims that the Rosetta contractors promised him safe passage. The U.S. attorney’s office has denied authorizing the deal.