BOGOTA, Colombia (AP) - Battle lines are being drawn over the massive fumigation of drug crops in Colombia, with opponents saying it poses health risks while the U.S. ambassador warns that aid could be withheld if the Washington-backed plan is scrapped.

The country's top anti-narcotics enforcer, meanwhile, is accusing drug traffickers - who have lost of millions of dollars in profits - of waging a smear campaign against Washington's $1.3 billion counterdrug offensive.

"What I have seen is a plot against the fumigations," Gen. Gustavo Socha, chief of the anti-narcotics police, told The Associated Press on Saturday. "The drug traffickers are generating false information and forcing people to disseminate it."

Though he did not provide specific examples, Socha said drug traffickers were forcing peasants to give false testimony about alleged illnesses from the sprayings.

Farmers and a coalition of governors from southern Colombia are demanding an end to the fumigation. The governors have visited the U.S. Congress to make their case.

The fumigation drive, in which planes spray herbicide on drug crops protected by leftist rebels and rival paramilitary forces, is the key to Washington's strategy to curb drug production in Colombia. This South American country is the leading supplier of cocaine and heroin to the United States.

The campaign has drawn increasing fire in recent weeks from critics who say the chemicals dropped from the planes are not only harmful to people, but are polluting one of the world's richest ecosystems.

A judge in Bogota on July 27 ordered a temporary halt of the spraying in Amazonian Indian lands, but he ruled Monday that the fumigation could resume. Judge Gilberto Reyes said the Indian group whose complaint had prompted the halt had failed to provide evidence to support its claim that spraying was causing health problems and environmental damage.

Underscoring U.S. concern about efforts to stop fumigation, Ambassador Anne Patterson warned that a permanent halt could jeopardize support for further aid in Washington.

"I am very scared that if the fumigation in Colombia doesn't continue, we won't give the level of assistance that Colombia needs," she told journalists on Monday.

Patterson did not elaborate on what assistance would be cut. Washington's $1.3 billion contribution to President Andres Pastrana's anti-drug offensive, dubbed Plan Colombia, is already in the pipeline.

It is paying for dozens of Blackhawk and "Super Huey" helicopters to ferry troops to drug-producing regions controlled by Colombia's illegal armed groups. The rival groups, along with the government, are embroiled in a 37-year civil war fueled by the drug trade.

The U.S. funds are also bankrolling social programs in Colombia.

For some, the debate recalls Washington's "big stick" approach to Latin America of times past.

In the respected Bogota newsmagazine Cambio, columnist Roberto Pombo alleged the sprayings were destroying the environment and impoverishing the country's peasant farmers, who have few or no viable alternatives to making a living other than growing drug crops.

Pombo called the fumigations a "failed campaign against drug traffickers, all by imperial order from the United States."

However, Pastrana had sought the assistance, and a groundswell of public opinion against the fumigation offensive, slated to continue over at least the next three years, has not materialized.

U.S. officials insist the herbicide, glyphosate, which is produced by the U.S. chemical company Monsanto, is safe. But the British company Imperial Chemical Industries confirmed Friday it has stopped supplying an additive used with the glyphosate, saying that use of the two agents together had not been tested.

The crop dusters, many provided by the State Department and flown by American contractors, have blanketed 123,500 acres of cocaine-producing crops since the campaign was launched last December in southern Putumayo province, Colombia's cocaine heartland.

Recent U.S. estimates showed 336,400 acres of coca, the main ingredient in cocaine, were being cultivated in Colombia. Colombian police say 15,300 acres were being used to grow poppy, from which heroin is made.