Delegates from 140 countries gather in Montreal this week to try to write a rule book to govern the world's ever-expanding trade in genetically altered organisms--grains, bacteria, farm animals--with life codes that have been rearranged in hopes of improving on nature's work.

The official focus will be safety: whether these creations could accidentally cause illness or harm to the environment. But underlying much of the talk will the issue of money and jobs.

The United States and a handful of other countries that pioneered the genetically modified organisms (GMOs) will press for relatively loose control of the trade. Countries that fear their farmers will lose out by not producing such high-yield crops will seek stronger standards.

Some of the protesters who disrupted the meeting of the World Trade Organization in Seattle late last year were angry about gene-altered foods. The questions are so contentious that a gathering on the issue in Cartagena, Colombia, last year ended in disarray, with the United States and its allies arrayed against most of the world.

In Montreal, about 300 opponents of genetically modified food braved winds and sub-zero temperatures Saturday in a peaceful march near the meeting site. Starting today, the delegates will try again to reach agreement on a Biosafety Protocol.

The outcome could have a big impact for U.S. farmers, who last year rang up sales of nearly $50 billion with the outside world. More than one-third of all cotton, corn and soybeans planted in the United States last year were bio-engineered varieties. Big yields from low-cost bio-engineered products give American farmers an advantage and the Clinton administration is anxious to keep their markets open.

"The world as a whole stands to benefit from a sound framework for management of bio- engineered products," said David Sandalow, assistant secretary of state for oceans, environment and science and U.S. delegation chief. "The world as a whole stands to lose if we impose draconian rules that cost billions of dollars, for little benefit."

Since the 1970s scientists have been tinkering with the basic genetic codes of plants and animals. Suburban Maryland is a national center of the growing industry, which seeks to create better crops, livestock and drugs through the manipulation of DNA, the basic life code.

Creators of the products describe them as crucial to feeding an ever-expanding global population (6 billion and counting), lowering malnutrition and taming now-incurable diseases. With proper testing and regulation, biotechnology products are safe, they contend, adding that the world has no choice but to adopt them.

Last week, for example, researchers announced they had created a new "golden rice," that contains transplanted genes to combat vitamin A deficiencies that can cause blindness in millions of children around the globe.

With hardly anyone noticing, genetically altered foods have entered the mainstream American diet and the world's diet.

In the 1990s backlash emerged, led by consumer groups, politicians and environmentalists who say the products are being rushed to market without adequate testing. What, they ask, if there are hidden health risks to humans? What if crops modified to be pest-resistant end up creating destructive strains of "super weeds" in the wild? A report last year that corn altered to kill pests also killed popular monarch butterflys aided naysayers.

For now Western Europe is the world's stronghold for this thinking. Both in government and in private activist groups, people praise "the precautionary principle," a fancy way of saying "better safe than sorry." While U.S. officials argue that there is no real evidence that the products are dangerous, Europeans say there is no real proof that they are safe and have blocked entry of new products.

In the United States, activists are trying to promote similar concerns against what they "genetic pollution." Some have an anti-capitalist bent, seeing genetic engineering as a new way in which giant corporations turn agriculture into Big Business and drive small farmers off their fields.

The Montreal talks grew out of the 1992 Earth Summit in Rio de Janeiro. At the summit countries agreed to regulate trade in "living modified organisms" to avoid harm to health or the environment. So far 176 countries have signed on to the resulting Convention on Biological Diversity. Though the Clinton administration supports the agreement, it was never ratified by the Senate, so the United States will be in Montreal with observer status. But as the world's largest farm good exporter, what it says is closely listened to.

A key issue on the table is whether and how countries should be notified if GMO products are being shipped to their shores. In leading the Miami Group of big farm exporters, which includes Canada, Chile, Argentina, Uruguay and Australia, the United States is expected to argue for a comparatively free approach.

U.S. negotiators say they would agree to a formal notification system for a limited group of products that they consider to be truly living organisms--seeds and animals, which would be introduced into the environment.

But the Clinton administration is opposed to something Europe, most developing countries and the activist community also want: prior notification on products such as grain that are intended just for consumption. Japan will start requiring labeling on some altered product next year and some importers are asking suppliers to notify them about the use of GMOs.

"Every country has the right to know in advance what's coming into their country," said Jeremy Rifkin, who has led a campaign critical of bio-engineering. "That's the sovereign right of farmers and consumers, to be able to turn down anything they don't want . . ."

U.S. delegation chief Sandalow said that such a system would seriously disrupt world trade in food, requiring billions of dollars of investment at ports and grain facilities, and for very little benefit.

Adrian Bebb of Friends of the Earth International, an Amsterdam-based environmentalist group, sees the United States as merely trying to protect the export earnings of its farmers.

Clearly, the argument at Montreal will not not only be about science. In many countries, stoking fear of genetically modified food can serve old-fashioned protectionist ends.

The Montreal meeting also will discuss whether a new protocol should override the rules of the WTO and how financially liable companies should be if their products cause harm.