PARIS: European Union environment officials have determined that two kinds of genetically modified corn could harm butterflies, modify food chains and disturb life in rivers and streams, and they have proposed a ban on the sale of the seeds, which are made by Pioneer Hi-Bred, Dow Agrosciences and Syngenta.

The preliminary decisions, seen by the International Herald Tribune, are circulating within the European Commission, the EU executive, which has the final say. Some officials there are skeptical about a ban that would upset the powerful biotechnology industry and could exacerbate tensions with important EU trading partners like the United States.

In the decisions, the EU environment commissioner, Stavros Dimas, says that the genetically modified corn, or maize, seeds - which are not now available on the European market for cultivation - could affect certain butterfly species, specifically the monarch, and other beneficial insects. For instance, research from 2007 indicates that larvae of the monarch butterfly exposed to the genetically modified corn 'behave differently than other larvae.'

In the decision concerning corn seeds produced by Dow and Pioneer, Dimas calls 'potential damage on the environment irreversible.' In the decision on Syngenta's corn, Dimas says that 'the level of risk generated by the cultivation of this product for the environment is unacceptable.'

A decision by the EU to disallow cultivation of the genetically modified crops would be the first of its kind in the trade bloc, making the current battle over genetically modified corn ferocious.

Since 1998, the commission has not approved any applications for the cultivation of genetically modified crops - but neither has the commission actively rejected any applications, as would be the case with the genetically modified corn products.

Banning the applications for corn cultivation also would mark a bold new step for EU environmental authorities, who already are aggressively pursuing regulations on emissions from cars and aircraft that have set it at odds with the United States and angered industries.

'These products have been grown in the U.S. and other countries for years,' said Stephen Norton, a spokesman for the United States Trade Representative. 'We are not aware of any other case when a product has been rejected after having been reviewed and determined safe by' European food safety authorities, Norton said.

In 2005, the European Food Safety Authority, a European agency based in Parma, Italy, that operates independently of the commission, ruled that the products - 1507, produced by Dow and Pioneer, and Bt11, produced by Syngenta - were unlikely to have an adverse effect on human and animal health or the environment. In the draft decision, Dimas said that other studies had since come to light on the potential effects of the seeds, and that further investigation was needed.

Environmentalists are seizing on the issue, too.

On Wednesday they called on Jose Manuel Barroso, president of the European Commission, to resist delaying the date for a meeting where the bans could be decided on, and they told him that a ban would have the support of many members of the European public.

'We believe that all commissioners should be given the right to express their views on this matter, which is of great concern to European citizens in all member states,' Jorgo Riss, director of the European unit of Greenpeace, wrote in a letter to Barroso co-signed by Friends of the Earth and a number of other groups dedicated to farmers and consumers. 'The vast majority of European citizens and consumers are opposed to genetically engineered plants in agriculture and for food,' Riss wrote.

Barbara Helfferich, a spokeswoman for Dimas, declined to comment on the specifics of the procedure because commissioners had not yet made a final decision. But she said that the EU was within its rights to make decisions based on the 'precautionary principle,' even when scientists have found no definitive evidence proving products can cause harm.

'The commission has the authority to be a risk manager when it comes to the safety and science of genetically modified crops,' said Helfferich.

She said that the decisions by Dimas could go before the commission within the next few weeks, but she, as well as a spokesman for Barroso, said that no date had yet been set.

In the decisions, Dimas cited research from 2007 showing that consumption of genetically modified 'corn byproducts reduced growth and increased mortality of non-target stream insects' and that these insects 'are important prey for aquatic and riparian predators' and that this could have 'unexpected ecosystem-scale consequences.'

Although still preliminary, Dimas's decisions could dramatically tilt the EU policy against future approvals of genetically modified crops, said Nathalie Moll, a spokeswoman for Europabio, an industry group with 80 members including Syngenta, Pioneer and Dow.

The decisions 'would be setting a precedent for EU officials to reject products based on nonverified scientific data,' said Moll.

Europabio says that the crops grown using the genetically modified corn already are imported into several EU countries, including France and Germany, where they are used to feed animals like cows and chickens.

Rob Gianfranceschi, spokesman at the U.S. Mission to the EU in Brussels, said it was too early to comment on a decision that had not yet been formalized. But he made clear that the United States remained frustrated with EU policies on genetically modified crops.

'The United States has consistently stated that the EU continues to lack a predictable, workable process for approving these products in a way that reflects scientific rather than political factors,' Gianfranceschi said.

Last year, in a victory for the United States, Canada and Argentina, the World Trade Organization ruled that the EU was wrongly delaying approvals of genetically modified products and that some countries, like Austria and Hungary, were wrongly banning the import and cultivation of crops.

Moll said the industry still was waiting to see whether the United States and Canada decide to retaliate against the EU for its policies on genetically modified crops.

Only one genetically modified crop is currently grown in Europe, a form of corn produced by Monsanto and nine other companies. Spain began growing that crop 10 years ago, followed by France, the Czech Republic, Poland, Slovakia, Romania, Portugal and Germany. But in a major blow to the biotechnology industry in France, President Nicolas Sarkozy last month vowed to suspend the cultivation of genetically modified crops.

Austria, Hungary and Poland also have banned the Monsanto corn, according to Greenpeace.

Moll of Europabio said the two genetically modified corn varieties Dimas proposed to ban are engineered to produce a toxin, commonly called Bt, that is poisonous to certain insect pests that lodge inside cobs and stalks and eat the plant from the inside. Protecting plants from these insects is important, she said, because the damage leaves the plants open to attack by fungi that produce a different toxin, fumonisin, which can enter the food chain and make products like milk unusable.

'Farmers in Europe must see a benefit in Bt corn because it protects against attacks by one of the major maize pests in Europe,' said Moll, adding that there had been a 77 percent increase in cultivation over the past year. Even so, corn represents only 14 percent of European agriculture, with the genetically modified product representing just 1 percent of that amount.

Across the rest of the world, said Moll, more than 200 genetically modified crops are being grown in countries from the United States to the Philippines.