The farm and pharmaceutical lobbies have blocked all meaningful efforts to reduce the use of antibiotics in raising livestock in the United States, a practice that contributes to an increasingly urgent public health risk, a study released Tuesday found.

Congress has killed every effort to restrict the feeding of farm animals the same antibiotics used in human medicine, the study says, even as antibiotics have grown less effective in treating infection. And regulation has gotten weaker under the Obama administration.

“Our worst fears were confirmed,’’ said Bob Martin, executive director of the Johns Hopkins Center for a Livable Future, which issued the report. The Food and Drug Administration’s statistics, he said, show that as much as 80 percent of the antibiotics sold in this country are fed to food animals.

The Centers for Disease Control and Prevention issued a report last month that found that 23,000 people die from antibiotic-resistant infections each year. The more a particular germ is exposed to antibiotics, the more rapidly it can develop resistance. Most scientists agree that overprescribing the drugs to humans is the predominant cause for bacteria evolving to outsmart them. Feeding the drugs widely to control and prevent disease in cows, pigs and chickens also is believed to play a role.

Tuesday’s study, “Industrial Food Animal Production in America,” comes five years after a landmark report on industry practices by a Pew Charitable Trusts commission of scientists working through the Johns Hopkins Bloomberg School of Public Health. Feeding animals antibiotics for breakfast, lunch and dinner plumps them up at a terrible cost, the 2008 report said, making drugs ever-less effective and bacteria more resistant.

FDA guidelines in the pipeline, Martin said, would require the industry to stop using antibiotics specifically to bulk up food animals but would continue to allow their use for disease control. But what constitutes disease control is so loosely defined, Martin said, that there would be no practical change in the use of antibiotics.

“In a couple of areas, the Obama administration started off with good intentions. But when industry pushed back, even weaker rules were issued,” he said. “We saw undue influence everywhere we turned.”

The report was authored by a commission that included ranchers, experts in public health and veterinary medicine, and former U.S. agriculture secretary Dan Glickman. Former Kansas governor John Carlin chaired the panel.

A spokeswoman for the Animal Agriculture Alliance, Emily Meredith, said producers “tend to disagree with much of what is said in the report,” have made significant progress over the past decade and have for years been using antibiotics judiciously.

The alliance, a coalition of food producers, released its own report on industry practices on Monday, defending modern farming techniques as necessary and ethical to feed a growing global population.

“Food safety in this country is the best it has ever been,” Richard Raymond, a former undersecretary for food safety and inspections at the Agriculture Department, wrote in the report’s foreword.

Antibiotics are part of set of biologic tools that have enabled producers to raise livestock in ways that are environmentally conscious and more humane, according to the report. “The vast majority” of antibiotics approved by the FDA for use in poultry and egg production are not used in human medicine “and therefore have little to no effect on the contribution to antibiotic resistance in humans,” the report said.

The FDA’s plan to address the issue “is to phase out the use of medically important antibiotics in food animals for growth promotion and feed efficiency,” Shelly Burgess, an agency spokeswoman, said via e-mail. “FDA believes these drugs should be used only in situations where they are necessary for treating, controlling, or preventing a specifically identified disease, and only under the oversight of a veterinarian.”

The Johns Hopkins report says the definition of “oversight by a veterinarian” has been changed, too, and no longer means much.

The FDA also has a strategy, wrote Burgess, to “effectively phase out production uses of medically important antimicrobials” and “has worked closely with stakeholders, including the pharmaceutical industry, animal producers, veterinarians, consumer groups, and public health organizations to ensure the success of this strategy. However, FDA’s approach does not rule out future regulatory action to ensure the judicious use of these important drugs.”

Rep. Louise M. Slaughter (D-N.Y.), a microbiologist by training, has been trying for 14 years to get Congress to pass the Preservation of Antibiotics for Medical Treatment Act. “No way” is the Republican-controlled House going to take up her proposed legislation, she said in an interview Monday. But it didn’t pass when Democrats were in control, either.

Mary Wilson of the Harvard School of Public Health said the risk to human health is real and immediate. “We will see common infections become fatal,” just as they were before the invention of antibiotics, she said.

She and other report authors said at a Tuesday news conference that the public has no idea how much the practice of modern medicine depends on antibiotics. When farmers in Denmark improved the conditions in which animals are raised, they said, they found they no longer needed to use antibiotics just to keep livestock alive until they were ready to slaughter.

In this country, regulators as well as lawmakers have long given in to industry pressure, according to Slaughter. In the 1970s, the FDA announced that the two classes of antibiotics used then in both human medicine and livestock production should not be routinely fed to animals. But the agency has been backpedaling since, she said, “because the lobbying on this is fierce.”

Another of the report’s authors, Michael Blackwell, a former dean of the College of Veterinary Medicine at the University of Tennessee at Knoxville, was more sympathetic to the challenges facing regulators. “Most of the people I’ve known over the years at the FDA think we have a horrible situation” in industrial animal production, he said, adding, “They live in this country, too,” and want their children eating food that is safe.

Without enough real authority to force producers to do anything, Blackwell said, “what they’re doing right now is almost pleading, in their own FDA-ish way,” with industry.

The only good news, the authors agreed, is that as consumers become more aware of how food is produced, they may demand changes.