The analysis by researchers at Stanford University, posted yesterday on the Web site of the Proceedings of the National Academy of Sciences, seeks to quantify security weaknesses in the nation's milk-supply chain and makes recommendations for closing those gaps.

Although some suggested changes are underway, federal officials felt the material had enough potential for misuse to warrant a last-minute effort to halt publication. That effort, which delayed the report's release by a month but ultimately did not keep it from becoming public, proved to be as contentious as the publication itself. It has assured the report's place in the scientific canon as one of the first test cases of how to balance scientific freedom and national security in the post-Sept. 11 era.

Study leader Lawrence M. Wein, whose previous research had forecast the likely effects of terrorist attacks involving anthrax and smallpox, said he was surprised by the government's push to block publication, which involved a flurry of phone calls and meetings with officers of the National Academies. The organization advises the federal government on matters of science and publishes the journal.

Last fall, Wein said, he briefed high-ranking officials of the departments of Homeland Security and Health and Human Services, along with dairy industry representatives, on his work.

"It was clear the dairy people were nervous about this paper coming out," Wein said. But when federal officials did not follow up, he said, he assumed they had concluded -- as had every reviewer at the National Academies -- that the information in the article was publicly available and easily obtained through a Google search.

Bill Hall, a spokesman for HHS, said yesterday that his department still opposes publication but was not in a position to block release of the data, which are not classified.

"We don't see eye to eye on this," Hall said. "If this ends up being the wrong decision down the road, the consequences could be quite severe and HHS will have to deal with it, not the National Academies."

The analysis by Wein and graduate student Yifan Liu considered what might happen if terrorists poured into a milk tanker truck a couple of gallons of concentrated sludge containing as much as 10 grams of botulinum toxin, a potent bacterial nerve poison now popular in low doses as a wrinkle eraser.

Because milk from many sources is combined in huge tanks holding hundreds of thousands of gallons, the toxin would get widely distributed in low, but potentially lethal, concentrations and within days be consumed by about 568,000 people, the report concludes.

The researchers acknowledge that their numbers are very rough. But depending on how thoroughly the milk was pasteurized (which partially inactivates toxins) and how promptly the outbreak was detected and supplies recalled, about 400,000 people would be likely to fall ill, they conclude.

Symptoms of botulism food poisoning arise within hours and progress from cramps, nausea and vision problems to paralysis and death by asphyxiation. Although only 6 percent of victims would generally be expected to die, the death rate could easily hit 60 percent, they conclude, because there would not be nearly enough mechanical ventilators or doses of antitoxin to treat so many victims.