With a midnight deadline drawing near, negotiators from 140 countries picked up the pace today to try to complete the world's first rule book for trade in genetically modified food and organisms. The major hang-ups: policy differences that pit the United States and a small group of allies against the rest of the globe.

Negotiators huddled in hotel rooms and corridors to patch together the "Biosafety Protocol." An effort last year to finish the job deadlocked over U.S. opposition on many of the same issues facing this gathering.

In 4 1/2 days of talks here, delegates have reached general agreement to create a Biosafety Clearing House, to which countries would report development of new genetically engineered products. Countries shipping altered seeds or other products intended for introduction into the environment would formally notify the receiving country.

Delegates have stumbled, however, over whether genetically engineered food should be treated that way as well. Many countries say yes, that altered food should be segregated and marked when it comes into their ports. The United States contends that this would be prohibitively expensive and serve no purpose.

At the same time, some U.S. grain-trading companies are starting to supply non-engineered crops on a special-order basis. The U.S. side of the talks is proposing that the question of documenting the food be put off for several years. The logic goes that if more companies opt to document it on their own, the United States would then be less likely to oppose rules requiring that practice.

The last-minute negotiating is reminiscent of the final day of talks at the World Trade Organization conference in Seattle late last year. That meeting ended in failure, but the mood here is considerably more upbeat.

U.S. farmers increasingly grow and export crops with genetic codes that have been altered to create higher yields and lower costs of production. Washington contends that the foods are adequately tested to safeguard against health or environmental problems and is anxious to keep those foreign markets open.

Much of the rest of the world is more skeptical and wants relatively tight regulation, contending that it's not really clear the products are safe. Europe has enacted laws requiring that engineered food be labeled so that consumers can make their own choices. Mixed in with environmental concerns are fears by some foreign farmers that the new crops will put them out of business.

Other friction involves the relationship of rules under discussion here to ones that govern general trade and the Geneva-based World Trade Organization.

The U.S. team was pressing for language that would make clear that countries would have to continue to respect their WTO obligations for market-opening. Washington fears that without this, some countries would use environmental concerns to keep out foreign farm goods when the real motivation was protectionism. Opponents contend that the United States wants to use WTO rules to force countries into taking food that is environmentally unsafe.

Also dividing the talks is the U.S. position that controls on products must be based on "sound science." Most of the rest of the world salutes "the precautionary principle," which holds that controls can be enforced even if there is not yet conclusive proof of problems. U.S. delegates tonight were trying to insert language specifying that there had to be some scientific basis to any precaution.

With the deadline closing in, politics was entering the mix, said Tewolde Berhan Gebre Eghziabher, an Ethiopian delegate who has spoken for most of the developing world. Negotiators are checking in with their governments. "The Washingtonians are calling Washington, the Ottawans are calling Ottawa," he joked.

"It's all possible, if people want it to happen," said Michael Williams, spokesman for the United Nations Environmental Program, which is sponsoring the talks.

CAPTION: A Greenpeace protester scales past a representation of a corn monster during global biosafety talks in Montreal.