Colombian and American officials acknowledge the obstacles, but they already cite modest success in eradicating heroin poppies in Colombia through alternative development.

Because of improved cooperation, Mexico eradicated large areas of heroin poppies and marijuana crops and reduced flights of large cargo jets carrying drugs over Mexico.

An additional 14,000 acres are used for growing heroin poppies, another illicit crop that is booming despite the American-financed spraying campaign.

But the same factors that make heroin poppies hard to eradicate also make it hard even to determine exactly how much exists, or exactly how much is winding up in the United States.

Growing heroin poppies is also increasing, experts say, though the poppies cover just several thousand acres.

The aid would also be used to help farmers grow alternative crops to coca leaf and heroin poppies and to bolster government programs to improve human rights.

Despite those goals, Colombian crops of coca leaves and heroin poppies have doubled in four years.

This, they say, is especially so because of both countries' proximity to the "Golden Triangle" of Burma, Laos and Thailand, where much of the world's heroin poppies are grown.

Some officials said they worried that while the Administration concentrated on limiting cocaine production and shipments from the Andean countries, cultivation of heroin poppies was rising in Guatemala and Mexico.

There, he spent six years in charge of drug-eradication efforts in Guerrero, the state that is Mexico's leading producer of heroin poppies.