BUDAPEST, Hungary — NATO defense ministers today authorized troops in Afghanistan to attack drug barons blamed for pumping up to $100 million a year into the coffers of resurgent Taliban fighters.

"With regard to counter-narcotics ... ISAF can act in concert with the Afghans against facilities and facilitators supporting the insurgency," said NATO spokesman James Appathurai, referring to the NATO force.

The United States had been pushing for NATO's 50,000 troops to take on a counter-narcotics role to hit back at the Taliban, whose increasing attacks have cast doubt on the prospects of a Western military victory in Afghanistan.

However, Germany, Spain and others were wary and their doubts led to NATO imposing conditions on the anti-drug mandate for the NATO-led International Security Assistance Force.

Troops will only be able to act against drug facilities if authorized by their own governments. Only drug producers deemed to be supporting the insurgency will be targeted, and the operation must be designed to be temporary — lasting only until the Afghan security forces are deemed able to take on the task.

NATO defense ministers will review the success of the mission when they next meet in February in Poland. Despite the limitations, U.S. Defense Secretary Robert Gates welcomed the NATO move.

Germany and Spain agreed to the anti-drug mission after an appeal for help from Afghanistan's defense minister.

Afghanistan supplies 90 percent of the world's heroin, a trade worth billions of dollars.

Until now, responsibility for dealing with the problem has lain with the Afghan police, but NATO commanders believe the fledgling force cannot cope with the problem. They say the time has come for NATO to move against the drug barons.

Some allies were concerned that a counter-narcotics campaign could spark a backlash against their troops, even if, as NATO commanders insist, the campaign will not target farmers who depend on growing opium poppies for a living.

They also feared that widening the mission could overstretch the hard-pressed troops and undermine NATO's long-term goal of handing more responsibility to Afghan forces.