Designed to cover half the surface area of a pack or carton of cigarettes, and a fifth of any advertisements for them, the labels are intended to spur smokers to quit by providing graphic reminders of tobacco’s dangers. The labels are required under a law passed last year that gave the Food and Drug Administration the power to regulate, but not ban, tobacco products for the first time.

Public health officials hope that the new labels will re-energize the nation’s antismoking efforts, which have stalled in recent years. About 20.6 percent of the nation’s adults, or 46.6 million people, and about 19.5 percent of high school students, or 3.4 million teenagers, are smokers.

Every day, about 1,000 children and teenagers become regular smokers, and 4,000 try smoking for the first time. About 440,000 people die every year from smoking-related health problems, and the cost to treat such problems exceeds $96 billion a year.

Some cigarette manufacturers vowed to fight the labels in federal court, saying they infringe the companies’ property and free-speech rights. A federal judge in Kentucky ruled in January in a related lawsuit that the F.D.A. could require graphic warning labels but that a proposed restriction intended to eliminate attractive coloring from cigarette packaging infringes free speech. That ruling has been appealed.

“The use of graphic warnings makes no contribution to the awareness of these risks and serves only to stigmatize smokers and denormalize smoking,” said Anthony Hemsley, a vice president at Commonwealth Brands, the maker of USA Gold cigarettes.

Among the most arresting of the proposed labels is one in which a man exhales smoke through a hole in his neck. Some smokers who suffer cancer of the larynx must breathe through a tracheotomy instead of their nose or mouth. But the proposed labels are not as gruesome as some mandated in Europe, in which ghastly photos of blackened teeth and decaying mouths give a Halloween aspect to cigarette packs.

“Today marks an important milestone in protecting our children and the health of the American public,” Kathleen Sebelius, the secretary of health and human services, said Wednesday.

The United States was the first country to require tobacco products to bear health warnings, and all cigarette packages now sold in the country have modest ones like “Surgeon General’s Warning: Smoking Causes Lung Cancer, Heart Disease, Emphysema, and May Complicate Pregnancy.”

But 39 other countries have gone well beyond such brief warnings and now require large, graphic depictions of smoking’s effects. With Wednesday’s announcement, the United States — whose first European settlements in the 17th century helped to create and feed a global tobacco addiction — edged a step closer to joining those nations’ efforts to reduce the centuries-old epidemic of tobacco-related deaths.

“This is the most important change in cigarette health warnings in the history of the United States,” said Matthew L. Myers, president of the Campaign for Tobacco-Free Kids.

Studies suggest that pictorial warnings are better at getting the attention of adolescents than ones that feature only text; make smokers more likely to skip the cigarette they had planned to smoke and more likely to quit; and make adolescents less likely to start smoking.

But health officials said there was some evidence that the most gruesome images, while memorable, are dismissed sooner by smokers. Health Canada recently backed away from a plan to introduce even more gruesome warnings, earning the government a rebuke from the Canadian Medical Association Journal.

“Sometimes images that are not as graphic may be more powerful in terms of changing behaviors,” said Dr. Lawrence R. Deyton, director of the Food and Drug Administration’s Center for Tobacco Products.

The F.D.A. has hired a company to survey 18,000 smokers to determine which labels might be most effective in getting smokers to quit and preventing adolescents from starting. Results were expected to be published within weeks and will be used along with public and expert comments to help winnow the 36 proposed labels to 9 by June.

By Oct. 22, 2012, manufacturers will no longer be allowed to distribute cigarettes for sale in the United States that do not display the graphic warnings. They will be required to allocate all nine warnings evenly.

Dr. Howard K. Koh, the assistant secretary for health, said in an interview that the new labels were part of the Obama administration’s comprehensive tobacco control plan that includes $250 million to support state and local antitobacco efforts.

“We want to not only support the new F.D.A. regulatory authority but reinvigorate the national commitment to ending the tobacco epidemic,” he said.

Tobacco retailers may face challenges displaying the new packaging because many stores show only the tops of cigarette packs, where the warnings would be shown, obscuring the brands. And high-end tobacco shops, which make much of their money from cigars and loose tobacco, may not want the warnings near their more expensive products.

“It may end up being that we stop carrying cigarettes,” said Ben Blackman, manager of Georgetown Tobacco in Washington. Such a result, of course, would delight public health officials.

Dr. Margaret Hamburg, the F.D.A. commissioner, said the agency would continue to monitor the effectiveness of the labels even after choosing its final nine. And if it decided that a different label would perform better than one already chosen, the agency would make a change, Dr. Hamburg said.

“We’re trying to reach a range of subpopulations and figure out what works best for whom,” she said. “When the rule takes effect, the health consequences of smoking will be obvious every time someone picks up a pack of cigarettes.”

Dr. Richard D. Hurt, director of the Nicotine Dependence Center at the Mayo Clinic, said he was hopeful the labels would save lives, though he said a higher federal tax and tougher workplace restrictions were also needed.

“The evidence is that graphic labels do make a difference in enticing smokers to stop smoking,” he said.

Still, Dr. Hurt predicted that cigarette makers would devise ways to blunt the labels’ effects with slip covers and other packaging. “It’ll be interesting to see what they try to do,” he said.

Then help arrived from an organization called Dairy Management. It teamed up with Domino’s to develop a new line of pizzas with 40 percent more cheese, and proceeded to devise and pay for a $12 million marketing campaign.

Consumers devoured the cheesier pizza, and sales soared by double digits. “This partnership is clearly working,” Brandon Solano, the Domino’s vice president for brand innovation, said in a statement to The New York Times.

But as healthy as this pizza has been for Domino’s, one slice contains as much as two-thirds of a day’s maximum recommended amount of saturated fat, which has been linked to heart disease and is high in calories.

And Dairy Management, which has made cheese its cause, is not a private business consultant. It is a marketing creation of the United States Department of Agriculture — the same agency at the center of a federal anti-obesity drive that discourages over-consumption of some of the very foods Dairy Management is vigorously promoting.

Urged on by government warnings about saturated fat, Americans have been moving toward low-fat milk for decades, leaving a surplus of whole milk and milk fat. Yet the government, through Dairy Management, is engaged in an effort to find ways to get dairy back into Americans’ diets, primarily through cheese.

Americans now eat an average of 33 pounds of cheese a year, nearly triple the 1970 rate. Cheese has become the largest source of saturated fat; an ounce of many cheeses contains as much saturated fat as a glass of whole milk.

When Michelle Obama implored restaurateurs in September to help fight obesity, she cited the proliferation of cheeseburgers and macaroni and cheese. “I want to challenge every restaurant to offer healthy menu options,” she told the National Restaurant Association’s annual meeting.

But in a series of confidential agreements approved by agriculture secretaries in both the Bush and Obama administrations, Dairy Management has worked with restaurants to expand their menus with cheese-laden products.

Consider the Taco Bell steak quesadilla, with cheddar, pepper jack, mozzarella and a creamy sauce. “The item used an average of eight times more cheese than other items on their menu,” the Agriculture Department said in a report, extolling Dairy Management’s work — without mentioning that the quesadilla has more than three-quarters of the daily recommended level of saturated fat and sodium.

Dairy Management, whose annual budget approaches $140 million, is largely financed by a government-mandated fee on the dairy industry. But it also receives several million dollars a year from the Agriculture Department, which appoints some of its board members, approves its marketing campaigns and major contracts and periodically reports to Congress on its work.

The organization’s activities, revealed through interviews and records, provide a stark example of inherent conflicts in the Agriculture Department’s historical roles as both marketer of agriculture products and America’s nutrition police.

In one instance, Dairy Management spent millions of dollars on research to support a national advertising campaign promoting the notion that people could lose weight by consuming more dairy products, records and interviews show. The campaign went on for four years, ending in 2007, even though other researchers — one paid by Dairy Management itself — found no such weight-loss benefits.

When the campaign was challenged as false, government lawyers defended it, saying the Agriculture Department “reviewed, approved and continually oversaw” the effort.

Dr. Walter C. Willett, chairman of the nutrition department at the Harvard School of Public Health and a former member of the federal government’s nutrition advisory committee, said: “The U.S.D.A. should not be involved in these programs that are promoting foods that we are consuming too much of already. A small amount of good-flavored cheese can be compatible with a healthy diet, but consumption in the U.S. is enormous and way beyond what is optimally healthy.”

The Agriculture Department declined to make top officials available for interviews for this article, and Dairy Management would not comment. In answering written questions, the department said that dairy promotion was intended to bolster farmers and rural economies, and that its oversight left Dairy Management’s board with “significant independence” in deciding how best to support those interests.

The department acknowledged that cheese is high in saturated fat, but said that lower milk consumption had made cheese an important source of calcium.

“When eaten in moderation and with attention to portion size, cheese can fit into a low-fat, healthy diet,” the department said.

In its reports to Congress, however, the Agriculture Department tallies Dairy Management’s successes in millions of pounds of cheese served.