OTTAWA — Roman Catholic leaders have joined the Council of Canadians in a campaign against patenting genetically modified seeds.

Seed patenting erodes the rights of farmers and threatens biodiversity, says Roger Dubois, president of Peace and Development, a Catholic agency active in the Third World.

"Increased hunger will be the impact of patenting seeds,'' he said Thursday at a news conference.

Ottawa Archbishop Marcel Gervais said it is wrong to patent the sources of life.

"Food security for the world's hungry requires decentralizing control, yet biopatenting centralizes control.''

Eighty per cent of patents on genetically modified foods are owned by 13 transnational corporations, said Gervais

Activists contend that farmers in poor countries are lured into using patented seeds, sometimes with free samples, then wind up having to pay patent fees every time they replant their crops.

Genetically modified crops are becoming increasingly important for pest control, but have sparked much debate about unintended side effects.

There are concerns they may harm beneficial insects such as bees and butterflies, may cause the development of ``superweeds'' and lead to the loss of traditional seed varieties.

Defenders of genetically modified crops say they reduce reliance on chemical pest control, while offering other valuable traits such as frost-resistance.<

``This has had a tremendous impact on farmers throughout the world,'' said Saskatchewan farmer Percy Schmeiser, who has become known for his battle with biotech giant Monsanto.

Monsanto sued Schmeiser for growing genetically modified canola without paying the fees. He said the seed had blown onto his field.

Last year the Federal Court of Appeal ordered Schmeiser to pay $19,000 in damages and $153,000 in court costs to Monsanto.

Schmeiser says the battle took his life savings, but he is receiving donations from around the world, and seeking leave to appeal to the Supreme Court of Canada.

Nadege Adam of the Council of Canadians said 48 genetically modified crops have been approved in Canada without public debate. She said the issues should be settled by Parliament, not the courts.

She called on Prime Minister Jean Chretien to intervene at the World Trade Organization to try to stop such patenting.

The two groups have collected about 180,000 cards, signed by Canadians across the country, calling for federal action on the issue.

No comment could immediately be obtained from Monsanto or Trade Minister Pierre Pettigrew.