It's spring, the season when American farmers return to their fields with trucks, tractors, cultivators, and plows. Some of their machinery has seen better days, but at least one part of their operations is the very latest high tech: their seed.

In the United States, a whopping 85 percent of the soybeans, three-fourths of the cotton, and nearly half of the corn planted last year were super varieties whose genes have been manipulated in a laboratory. These and nearly a dozen other genetically modified (GM) crops - from papaya and potatoes to squash, sugar beets, tobacco, and tomatoes - have been altered by scientists to produce higher yields or to better resist herbicides, pests, or drought.

In all, an area larger than the state of California is under cultivation in the US with bioengineered crops. Most Americans consume these GM foods without a second thought - or a label telling of the GM content. That's because the US government does not consider these changed crops to be different enough from their conventional counterparts to warrant special labeling.

Much of the world disagrees. In Europe and parts of Africa and Asia, concern about GM crops is much higher, and governments are setting stricter standards. By contrast in the US, the technology is not only moving forward, the battleground has shifted.

Instead of pushing for nationwide labeling, opponents have moved to the state and local levels. This has made the debate less visible and changed its nature from primarily a consumer-driven controversy into a producer-driven one. Concerns center on the technology's economic impact on organic farmers and foreign sales, as well as on the benefits and dangers of producing drugs and industrial compounds in farm fields.

"What we see is that the states are the battleground for a lot of these conflicts that the introduction of biotechnology has created," says Michael Rodemeyer, executive director of the Pew Initiative on Food and Biotechnology, a nonpartisan think tank in Washington, D.C. States see big opportunities for economic growth with this "very promising technology," he says. But they're also "very concerned about protecting their existing agricultural base," meaning they want safeguards that GM crops won't accidentally mix with other crops or acquire their traits, such as resistance to herbicides.

In all, 35 states introduced some kind of GM crop legislation in 2003-2004, according to statistics compiled by the Pew Initiative. A total of 170 bills and resolutions were introduced and 37 passed, about 22 percent.

In California, counties have banned GM crops, saying that they would reduce the value of local organic produce. "A lot of the anti-GM and pro-organic communities feel that they have more power at the local and county levels than they do at the state level," Mr. Rodemeyer says.

Encouraged by pro-biotech forces, states are countering by passing laws that ban local regulation of GM crops. In 2004, South Dakota and Pennsylvania enacted such laws. This spring, six more states joined them, according to the Pew Initiative: Georgia, Idaho, Indiana, Iowa, Kansas, and North Dakota.

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