Chinese regulators are calling out livestreamers who binge-eat for promoting excessive consumption. A school said it would bar students from applying for scholarships if their daily leftovers exceeded a set amount. A restaurant placed electronic scales at its entrance for customers to weigh themselves to avoid ordering too much.

China’s top leader, Xi Jinping, has declared a war on the “shocking and distressing” squandering of food, and the nation is racing to respond, with some going to greater extremes than others.

The ruling Communist Party has long sought to portray Mr. Xi as a fighter of excess and gluttony in officialdom, but this new call for gastronomic discipline is aimed at the public and carries a special urgency. When it comes to food security, Mr. Xi said, Chinese citizens should maintain a sense of crisis because of vulnerabilities exposed by the coronavirus pandemic.

“Cultivate thrifty habits and foster a social environment where waste is shameful and thriftiness is applaudable,” Mr. Xi said in a directive carried by the official People’s Daily newspaper last week.

Mr. Xi’s edict is part of a broader message from the leadership in recent weeks about the importance of self-reliance in a time of tensions with the United States and other economic partners. The concern is that import disruptions caused by the global geopolitical turmoil, the pandemic and trade tensions with the Trump administration, as well as some of China’s worst floods this year, could cut into food supplies.

But like so many top-down orders in China, the vaguely worded directive prompted a flurry of speculation. State news media moved quickly to tamp down panic about imminent food shortages, reporting that China had recently seen consecutive bumper grain harvests and record high grain output.

The edict was also met with sometimes ham-handed measures. The restaurant that offered to weigh patrons in the central Chinese city of Changsha quickly drew a backlash and was forced to apologize over the weekend.

“Our intention was to advocate not wasting food and for people to order in a healthy way,” the restaurant said. “We never forced customers to weigh themselves.”

Mr. Xi’s “clean plate” campaign strikes at the heart of dining culture in China. Custom dictates that ordering extra dishes and leaving food behind are ways to demonstrate generosity toward one’s relatives, clients, business partners and important guests.

Such habits have contributed to an estimated 17 million to 18 million tons of food being discarded annually, an amount that could feed 30 million to 50 million people for a year, according to a study by the Chinese Academy of Science and the World Wildlife Fund.

Mr. Xi’s call is as much a warning against the dangers of profligacy as it is a reflection of the generational shift in values that has emerged as living standards rise.

Austerity campaigns can seem out of place in modern China, where cities with gleaming skyscrapers and luxury malls buzz with fancy cars. But they were common in the era of Mao Zedong, when the People’s Daily would urge citizens to “eat only two meals a day, one of which should be soft and liquid.”

Wang Yaqin, a 79-year-old retiree in the northeastern Chinese city of Harbin, remembers the several years of famine precipitated by Mao’s disastrous Great Leap Forward campaign from 1958 to 1962. In that campaign, in which Mao ordered peasants to reorganize into communes and build backyard steel furnaces to catch up with the West, food supplies plummeted, officials falsely inflated grain harvests, and by some estimates 45 million people starved.

During those years, Ms. Wang said, there was little else to eat besides beet pulp — commonly used to feed horses and cattle — mixed with sweet corn noodles.

Though food is now plentiful, Ms. Wang remains uneasy with simply tossing it out. Once, she said, she even retrieved some dumplings that her children had thrown away, rinsing and eating them.

“This campaign is brilliant,” said Ms. Wang in a telephone interview. “Although it seems like a small thing, it’s good if even one watt of electricity and one drop of water can be saved.”

Many among the country’s younger generation, such as Samantha Pan, a 21-year-old student in Guangzhou, embrace being free from having to worry about saving food for a rainy day, and hold little regard for the state’s moral exhortations.

“This type of initiative is very boring and useless,” Ms. Pan said in a telephone interview. “I am entitled to order as much food as I want. If I just happen to love wasting food, it’s still my freedom.”

For Mr. Xi, the issue of food security has taken on more importance as China grapples with overlapping crises including a shaky economy and severe floods that have left large swaths of the country’s farmland under water.

Food prices climbed about 13 percent in July compared with a year ago, according to official statistics. The price of pork, a staple food for many Chinese families, increased by about 85 percent during that same period, in part because the floods affected production and transportation.

Farmers in the central Chinese province of Henan, a crucial grain-producing region, admitted to stockpiling much of their grain harvests this year in the hopes of selling for higher prices later, according to a report published on Monday in the party-backed China Youth Daily newspaper.

As tensions with other countries have risen, the party has been girding itself for the possibility of being cut off internationally — and making sure it can produce enough food to feed China’s 1.4 billion people.

“In an ideal environment, international relations would be very good and China could freely import food from other places,” said Hu Xingdou, a Beijing-based political economist. “But practically speaking, China may have some big problems.”

Wu Qiang, a political analyst based in Beijing, said the pandemic and the floods were reminiscent of the challenges that dogged China’s emperors, whose legitimacy largely rested on their perceived ability to maintain harmony between humans and nature.

By taking steps to pre-empt a food shortage, Mr. Xi is showing that he recognizes the challenge these crises, if left unchecked, could pose to his hold on power, Mr. Wu said. “So now he’s pushing the responsibility onto the people, telling them to be thrifty,” he said.

But some restaurant owners are reluctant to bear the cost of Mr. Xi’s clean plate campaign.

Jimmy Zhang, the owner of a home-style restaurant in the city of Linyi, in the eastern province of Shandong, said he supported Mr. Xi’s call but didn’t want to encourage customers to order fewer dishes.

“What the country is promoting is good, but as a citizen, the policies are too far away from me,” said Mr. Zhang, adding that the costs of rent and employee salaries were rising. “There’s no way I can support them without losing money.”

The campaign also throws into question the entire business model driving a niche corner of the Chinese internet — livestreamers who have found fame by recording themselves eating vast amounts of food.

Known as “big stomach kings,” many such video bloggers draw hordes of fans and rely on these shows for income. China’s state-run broadcaster, C.C.T.V., slammed such performances in a recent commentary headlined: “Livestreaming is fine, but do not use food as your props!”

China’s biggest short-video and social media platforms — including Douyin, China’s version of TikTok, and Kuaishou — said they would punish users seen to be wasting food in their broadcasts.

A video blogger, who until recently went by the name “Big Stomach Mini” and once ate an entire roasted lamb in one meal, posted a new video on her social media page last week in which she urged her followers to savor every bite of food and take home leftovers. The video drew messages of support from some of her 11 million fans.

“There’s nothing wrong with enjoying delicious cuisine,” said the blogger, who has since changed her name to the more austere-sounding “Dimple Mini.” “But please don’t be extravagant and wasteful.”