For as far as the eye can see, stalks of sugar cane march across the hillsides here like giant praying mantises. This is ground zero for ethanol production in Brazil -- "the Saudi Arabia of biofuels," as some have already labeled this vast South American country.

But even as Brazil's booming economy is powered by fuel processed from the cane, labor officials are confronting what some call the country's dirty little ethanol secret: the mostly primitive conditions endured by the multitudes of workers who cut the cane.

Biofuels may help reduce humanity's carbon footprint, but the social footprint is substantial.

"These workers should have a break, a place to eat and access to a proper restroom," Marcus Vinicius Goncalves, a government labor cop in suit and tie, declared in the midst of a snarl of felled stalks and bedraggled cane cutters here. "This is degrading treatment."

More than 300,000 farmworkers are seasonal cane cutters in Brazil, the government says. By most accounts, their work and living conditions range from basic to deplorable to outright servitude.

"Brazil has a great climate, great land and technology, but a lot of the competitive edge for biofuels is due to worker exploitation -- from slave work to underpayment," said Leonardo Sakamoto, a political scientist who runs a nonprofit labor watchdog group in Sao Paulo.

In the last four years, said a lawyer from the Public Ministry, which acts as the Sao Paulo state district attorney, at least 18 cane cutters have died of dehydration, heart attacks or other ailments linked to exhaustion in this region, where the forests long ago gave way to agriculture.

That does not include an unknown number of others who died in accidents, said the lawyer, Luis Henrique Rafael, part of a two-attorney team from the Public Ministry's office that recently toured the area to investigate abuses of the labor code.

"They died from excess work," Rafael said. "Even prisoners have a better life. These men's only form of leisure is cachaca," he added, referring to the liquor distilled from sugar cane.

In its annual report, Amnesty International last month highlighted the plight of Brazil's biofuel workers, more than 1,000 of whom were rescued in June 2007 after allegedly being held in slave-like conditions at a plantation owned by a major ethanol producer, Pagrisa, in the Amazonian state of Para.

Although slavery cases tend to grab headlines, advocates say laborers typically face more quotidian abuse -- low pay, excessive work hours, inadequate safety gear, an absence of sanitary and health services, and exposure to pesticides and other toxic chemicals.

"The cases analogous to slavery seem not to be the norm," said Tim Cahill, Brazil researcher for Amnesty International. "But this is very much a case of long work hours, the destruction of workers' health through extreme conditions, a lack of access to quality food, problems of accommodation, and the impacts of agro-toxins."

The technological advances that have facilitated the biofuel revolution have not reached the fields. Although mechanized harvesting of cane is on the rise, rough terrain dictates that much of the crop must still be cut manually.

Industry officials acknowledge some abuses, but insist that safety has improved and that the allegations of slavery are greatly exaggerated.

"If there is an industry that has bettered the situation of the worker, it is the sugar cane industry," said Rodolfo Tavares of Brazil's National Confederation of Agriculture, a trade group. "It's an example for the world."

With international scrutiny growing, leftist President Luiz Inacio Lula da Silva says the government and producers are keen to ameliorate conditions.

"Everyone knows that sugar cane labor is tough," Lula said in Rome this month during a food crisis summit at which biofuels were called a major culprit. But "it's not tougher than labor in coal mines, which was the basis for the development of Europe. Take a big knife to cut cane and then go down in a mine, 90 meters deep, to explode dynamite. You'll see which is better."

Brazilian officials acknowledge that fines and prosecutions have largely failed to improve the workers' lot. Cases drag on in court until sanctions are reduced or owners cleared. Few, if any, violators go to jail. Too few inspectors are available to police this giant country and its behemoth agribusiness, which have made it a world leader in exports of soybeans, beef and coffee, among other foodstuffs.

In the last year, Brazil has stepped up cases filed under antislavery statutes, which can land offenders in prison. Authorities say that last year they "liberated" nearly 6,000 agricultural workers from slave-like conditions, which under Brazilian law can include debt servitude, forced labor and a "degrading" work environment. More than half toiled in the sugar cane sector.