OPPONENTS of genetically modified food were outgunned yesterday in one of the most important international conferences on the issue to date.

Buoyed after the Prime Minister's weekend acknowledgement of their fears, the environmental lobby was brought down to earth with a bump in Edinburgh.

They had said before the conference opened that the odds were stacked against them, and they appeared to be right.

For a start, most of the main speakers were scientists working on GM foods, with organisations like Friends of the Earth and Greenpeace relegated to discussion panels.

The goalposts were not the ones they wanted to aim at either. Greenpeace wanted to talk about the threat to the environment - the creation of untameable mutant weeds, and fauna like Monarch butterflies at risk of extinction.

However, the focus has been on the risks to human health. These are what the public are worried about but they are still ill-defined and unproven - there is only so much you can say about a leap in the dark.

Dr Arpad Pusztai, who left the Rowett Institute in Aberdeen under a cloud because of a study showing rats' organs being altered by GM potatoes, heard his work contradicted by a Chinese scientist who had done the same experiment with negative results.

That left the devil with all the best tunes - forecasts of how GM foods will combat disease and malnutrition throughout the world.

They were couched with some caution and some pointers to the kinds of tests that will be needed to ensure the safe introduction of GM produce.

However, the message that is likely to go back to the Economic Council on Co-operation and Development (OECD), who organised the conference, is how and when, rather than if, we will see GM foods on our shelves. According to Professor Marc Wecksler from Cornell University in the USA, genetically modified organisms will revolutionise nutrition in the less developed countries. Conventional injected vaccines are of limited use in developing countries because of the lack of refrigeration to store them or sterile needles and health workers to administer them. Professor Wecksler predicted this problem could be solved by putting the vaccines genetically into staple foods like rice.

''A million children die every year from measles even though there is a perfectly good vaccine,'' he said. ''Another food-borne vaccine against Hepatitis B could protect adults from liver cancer.

''Enriching food with nutrients could help the elderly fend off infections, save the millions who die worldwide from protein malnutrition, and protect children in the poorest countries from stunted growth.''

Taking out genes as well as putting them in could also make foods healthier, he pointed out. Gene coding for the molecules that cause food allergies could be removed - the ubiquitous warning ''may contain peanuts'' could lose its life or death importance.

Altogether, said Professor Wecksler, the old adage that an apple a day keeps the doctor away could become literally true.

However, a Greenpeace International delegate told the conference that hopes of solving malnutrition in the Third World with GM food could prove as illusory as the promise 40 years ago of cheap nuclear power. ''Billions have been spent developing nuclear power and billions more will be spent to - hopefully - control the problems that have arisen from its use,'' said Mr Benedikt Haerlin.

''These billions have been lost to the development of sustainable energy. The same things will happen with GM foods. Billions will be spent on GM technology and money which would have been better spent on developing existing food technology will be lost.

''We are already losing knowledge about conventional food technology and we might be facing the need for huge expenditure to solve the problems caused by the release of GM crops into the atmosphere.''

Mr Haerlin said that by concentrating on food safety and economics, the conference was trying to answer the second and third questions without answering the first.

''If we accept, as Greenpeace does, that GM crops should not be released into the environment, then we don't need to be sitting here talking about food safety.

''Greenpeace has come to the conclusion that the state of existing knowledge about the release of GMOs into the environment does not allow this release.''

He said this release would be irreversible: ''Every month we read in scientific papers things that cannot be explained. Is this the right time to be doing something that is irreversible? Should we try to understand what we are doing before we proceed or find out by trial and error?''