''This technology is an assault on the traditional knowledge, innovation, and practices of local and indigenous communities,'' said Debra Harry, executive director of the U.S.-based Indigenous Peoples Council on Biocolonialism.

The group is among organizations urging United Nations experts to recommend that governments adopt tough laws against field testing and selling Terminator technology, which refers to plants that have had their genes altered so that they render sterile seeds at harvest. Because of this trait, some activists call Terminator products ''suicide seeds.''

Developed by multinational agribusinesses and the U.S. government, Terminator has the effect of preventing farmers from saving or replanting seeds from one growing season to the next.

The product is being tested in greenhouses throughout the United States. Opponents fear it is likely to be marketed soon unless governments impose a ban.

''Terminator seeds will become a commercial reality unless governments take action to prevent it,'' said Hope Shand of the Canada-based Action Group on Erosion, Technology, and Concentration (ETC Group).

If commercialized, activists said, Terminator would force farmers to return to the market for seeds every year, adding to their annual costs. This also would spell the end of locally adapted agriculture through seed selection, because most farmers in the world today routinely save seeds from their harvest for replanting.

''This seed technology is a fundamental violation of the human rights of indigenous people,'' Harry said of Terminator. ''It is a breach of the right of self-determination.''

Environmental and consumer advocates also have said that genetically modified crops--ranging from Terminator to ''Round Up Ready'' varieties designed to survive the heavy duty herbicide Round Up--offer the promise of fat profits for their developers, marketers, and political supporters while threatening farmers with lean times and consumers with ill-health.

''The promise of increased profit is too enticing for industry to give up on Terminator seeds,'' says Lucy Sharratt of the International Ban Terminator Campaign.

The issue has pitted some governments against their citizens. Canadian government officials at a UN meeting in Bangkok last year pushed for language allowing the field testing and sale of Terminator. But they backed down in response to strong public criticism at home.

For their part, biotech companies have enjoyed limited success in trying to influence governments' policies in favor of using Terminator seeds. Their main argument: that Terminator's higher cost is more than compensated for in improved crop yield and quality at harvest time.

Governments generally have distinguished between different types of genetic modification. Many--especially those in industrially developing regions of the world--have resisted pressure from the biotechnology industry and the U.S. government and maintain a strong stand against Terminator.

The government of Brazil--the world's fifth most populous country and a major agricultural producer--last year enacted a law that prohibits the use, registration, patenting, and licensing of genetically modified (GM) seeds. India, a predominantly agrarian nation and home to more than one billion people, has done the same.

However, a number of governments have agreed with industry statements that other genetic modifications can play a significant role in combating hunger at negligible risk to the environment.

Even so, a 100-page report released last week by Friends of the Earth (FoE), a leading international environmental group, concludes that only a handful of countries have introduced and increased the use of genetically modified crops--and then again, largely because of aggressive lobbying by the biotech industry.

Entitled ''Who Benefits from GM Crops?'' the report says that after 10 years of GM crop cultivation, more than 80 percent of the area cultivated with biotech crops is still concentrated in only three countries: the United States, Argentina, and Canada.

In other countries--including Paraguay and Brazil, GM crops were planted illegally and in Indonesia, they were planted after government officials were bribed, FoE said.

This week's UN talks in Madrid are scheduled to continue until Friday.