RALEIGH, N.C. — Federal investigators have unraveled a massive scheme among dozens of insurance agents, claims adjusters, brokers and farmers in eastern North Carolina to steal at least $100 million from the government-backed program that insures crops.

Authorities say the ongoing investigation is already the largest such ring uncovered in the country.

Forty-one defendants have either pleaded guilty or reached plea agreements after profiting from false insurance claims for losses of tobacco, soybeans, wheat and corn. Often, the crops weren’t damaged at all, with farmers using aliases to sell their written-off harvests for cash.

Prosecutors compared the case to busting a drug cartel, where federal investigators used a confidential informant to ensnare a key participant in the sophisticated fraud, who then agreed to implicate others. That first wave of prosecutions led to still more names to investigate.

“These defendants make it harder on the honest farmer,” Assistant U.S. Attorney Banumathi Rangarajan said. “The more they lie and steal the more premiums and costs go up for the farmers who play by the rules.”

The federal crop insurance program was created during the Dust Bowl of the 1930s as a way to keep farmers from going bankrupt because of a bad growing season. The U.S. Department of Agriculture pays about 15 private insurers to sell and manage the policies, but taxpayers are on the hook for most of the losses. Payouts for 2012 have topped $15.6 billion — a figure that is still growing as new claims are filed.

Bruce A. Babcock, an agricultural economist at Iowa State University, said fraud likely accounts for a small percentage of that total.

“There’s always fraud in the crop insurance system, but I’ve seen nothing to suggest it is pervasive,” Babcock said. “Eighty percent of the program costs are supported by the federal government. Some people see defrauding taxpayers like cheating on their income taxes.”

Those prosecuted in North Carolina raked in millions for years without detection until 2005, when prosecutors say USDA auditors used computer software to mine insurance claims data from across the country for outliers. Among the names identified was Robert Carl Stokes, a Wilson crop insurance agent whose clients appeared to have consistently horrible luck.

Through prosecuting Stokes and his immediate co-conspirators, authorities were led to dozens of others involved in similar frauds throughout eastern North Carolina, with crooked claims adjusters and tobacco brokers working with multiple insurance agents and their farmer clients. The USDA’s Office of Inspector General said the recent string of crop insurance convictions in eastern North Carolina eclipses similar investigations anywhere else in the United States.

“Our agents have been involved in a remarkable number of successful crop insurance investigations in this district, with substantial monetary penalties and restitution ordered by the court,” said Karen Citizen-Wilcox, Special Agent-in-Charge of the Southeast Region.

USDA requires tobacco growers to take out crop insurance ahead of the growing season, but payment on those policies is not due until after the harvest. If the crop is damaged by bad weather or leaf-munching bugs, the farmer is paid the difference between the value of his diminished harvest and the amount of the policy.

According to Stokes’ indictment, the insurance agent recruited farmers to take out large policies and then claim large losses, even as they produced bumper crops. Stokes helped the farmers keep the true value of their harvests secret by selling “hidden” tobacco through warehouse operators in on the scheme, who agreed to write checks to false recipients to help obscure who was really getting the money.

Stokes would then cash the checks for the farmers, keeping a percentage. Stokes would also keep a share of the payout from the government-backed insurance settlement, according to prosecutors.

Charged with 14 felony counts, Stokes pleaded guilty in 2011 to two counts of conspiring to make false statements and to commit money laundering and was sentenced to 30 months in prison. He also agreed to pay more than $16.5 million in court-ordered restitution.

Released last month from a federal penitentiary in West Virginia, Stokes is back in Wilson wearing an electronic ankle bracelet that allows federal authorities to track his movements. He declined to comment on his conviction, citing the three years of probation remaining on his sentence. Now 62 and unemployed, he is paying $200 every month toward the millions he still owes in restitution.

Five years after Stokes’ arrest, crop insurance fraud cases continue to cycle through the federal courthouse in Raleigh.

Last month, former Rural Community Insurance Services adjuster Jimmy Thomas Sasser was sentenced to four years in prison and to pay more than $21 million in restitution.

According to prosecutors, Sasser for years took cash payoffs ranging from $400 to $2,000 to falsify claims for hail damage at the behest of Stokes and another convicted insurance agent, Mark Davis Pridgen. As part of his guilty plea, Stokes, 61, also admitted that he threated to kill Pridgen, his former brother-in-law, in retaliation for cooperating with investigators.

Now at home waiting for a spot to open up in a federal prison, Sasser said fraud is common in the crop insurance system, which offers limited ways for authorities to discover when loss estimates are exaggerated or falsified.

“I can tell you it’s everywhere, all across the country,” Sasser said Monday. “When you let the farmers keep up with their own production, they can put that production anywhere they want to. All the adjuster does is take what the farmer gives him to work the claim. What the farmer does before the adjuster gets there, the adjuster has no idea.”

Last week, the wife of Southern Pines tobacco broker Jesse Ray “Tommy” Faulkner softly wept in court as U.S. marshals handcuffed her husband after he violated the terms of his pre-trial release by getting arrested for driving while impaired in February. Facing two conspiracy counts, Faulkner is set to be sentenced later this month after entering a plea agreement that remains under seal.

Faulkner’s lawyer, Kindelle McCullen, had pleaded with U.S. District Court Judge James C. Dever III to delay the sentencing and allow her client to go to rehab for alcoholism, citing what she described as his extensive cooperation with federal investigators in pending crop fraud cases.

Dever was unmoved, sending Faulkner off to jail and indicating his desire to go ahead with sentencing.

“I know I’ve been sentencing a lot of folks in this scheme,” the judge said, “I’m ready to get on with it.”

Many of the dozens of defendants sentenced so far have received years in federal prison, agreeing to pay a total of $42 million in restitution and more than $900,000 in fines. That’s still less than half what federal prosecutors say taxpayers have been bilked.

Thomas Walker, the U.S. attorney for the Eastern District of North Carolina, said the investigation is continuing and that others may still be charged.

“Crop insurance fraud is the same as mortgage fraud and health care fraud,” Walker said. “It’s all about greed and stealing from the taxpayer. We aggressively pursue these criminals just like we pursue drug dealers and other crooks.”