MONTREAL (AP) _ In the final hours of international talks Friday on trade in genetically modified food and other products, negotiators found themselves grappling over the same issues that doomed a similar agreement nearly a year ago.

Delegates scurried from room to room of the Montreal hotel where the meeting was being held, bearing proposals and counterproposals. The shuttling delayed the start of a final plenary session for seven hours. When it finally began just before midnight, key U.S. and European delegates were not present _ still negotiating separately over their differences.

Mayr, who set a deadline of Friday night, has said that he will not leave Montreal without an agreement.

``Somebody has to give in somewhere,'' said Ethiopian head delegate Towalde Egziabher.

Negotiators were attempting to draft the Biosafety Protocol, a set of rules that would protect the environment from damage by genetically modified plants, animals and bacteria. Environmentalists and a few scientific studies have raised concerns that genetically modified organisms could wipe out native species, disrupt natural cycles and cause other ecological damage.

``There's fish genes in fruit, poultry genes in fish, animal genes in plants, growth hormones in milk, insect genes in vegetables, tree genes in grain and in the case of pork, human genes in meat,'' said Steve Gilman, an organic farmer in Stillwater, N.Y. ``Real and reasonable concerns about genetic engineering have fallen upon deaf ears.''

The debate at the talks has revolved around how great the scientific uncertainty is, and how it should be dealt with. The European Union and developing nations have argued that countries should be allowed to decline imports of a genetically modified product if little is known about its environmental effect.

But the United States and its partners disagree, saying the proposed rules in their current form would restrict trade. Those countries argued that any nation's refusal to import a genetically modified product should be backed by scientific evidence in the form of a risk assessment.

``We live in a world in which scientific certainty is not available,'' said U.S. Undersecretary of State Frank Loy.

Talks last February in Cartagena, Colombia, ended in disarray when the United States and five other countries _ Canada, Australia, Argentina, Chile and Uruguay _ rejected a draft agreement favored by 125 other countries.

The situation has changed since then, with major U.S. food producers such as Archer Daniels Midland, Gerber and the Iams pet food company either demanding that genetically modified products be segregated or refusing to use them altogether. Protests at the World Trade Organization talks in Seattle last month also suggest that the American public has concerns about genetically altered food.

``In the year since Cartagena, it has become obvious that the position of the (United States') group is increasingly isolated,'' said Philip Bereano, a University of Washington professor who has been following the talks.

Just as in Cartagena, the talks in Montreal have come down to a handful of issues:

_The relationship of the proposed rules to the World Trade Organization. The United States wants the agreement to have ``equal status'' with the free trade pact. But other countries fear that any bans they impose will be overturned by the World Trade Organization's dispute resolution panel.

_The amount of scientific evidence that is needed to justify banning a genetically modified product.

_The amount of evidence that exporters must provide about their products.

Genetically modified crops are already widespread. About 70 million acres of genetically engineered plants were cultivated worldwide in 1999. In the United States, genetically engineered varieties account for about 25 percent of corn and 40 percent of soybeans.