With food riots in some countries focusing attention on how the world will feed itself, biotechnology proponents see their chance. They argue that while genetic engineering might have been deemed unnecessary when food was abundant, it will be essential for helping the world cope with the demand for food and biofuels in the decades ahead.

Through gene splicing, the modified crops now grown  mainly canola, corn, cotton and soybeans  typically contain bacterial genes that help the plants resist insects or tolerate a herbicide that can be sprayed to kill weeds while leaving the crop unscathed. Biotechnology companies are also working on crops that might need less water or fertilizer, which could have a bigger impact on improving yield.

Certainly any new receptivity to genetically modified crops would be a boon to American exporters. The United States accounted for half the world’s acreage of biotech crops last year.

But substantial amounts of corn, soy or canola are grown in Argentina, Brazil and Canada. China has developed insect-resistant rice that is awaiting regulatory approval in that country.

The pressure to re-evaluate biotech comes as prices of some staples like rice and wheat have doubled in the last few months, provoking violent protests in several countries including Cameroon, Egypt, Haiti and Thailand. Factors behind the price spikes include the diversion of crops to make biofuel, rising energy prices, growing prosperity in India and China, and droughts in some regions  including Australia, a major grain producer.

Biotechnology still certainly faces obstacles. Polls in Europe do not yet show a decisive shift in consumer sentiment, and the industry has had some recent setbacks. Since the beginning of the year France has banned the planting of genetically modified corn while Germany has enacted a law allowing for foods to be labeled as “G.M. free.”

And a new international assessment of the future of agriculture, released last Tuesday, gave such tepid support to the role genetic engineering could play in easing hunger that biotechnology industry representatives withdrew from the project in protest. The report was a collaboration of more than 60 governments, with participation from companies and nonprofit groups, under the auspices of the World Bank and the United Nations.