SHANGHAI - It has been two years since China’s government, reeling from international outrage over melamine-contaminated baby milk that sickened 300,000 infants and killed at least 6, declared food safety a national priority. Since then, it has threatened, raided and arrested throngs of shady food processors - and even executed a couple.

But a stomach-turning string of food-safety scandals this spring makes it clear that official efforts are falling short.

“Most of them are working like headless chickens, having no clue what are the major food-borne diseases that need to be addressed or what are the major contaminants ,” said Dr. Peter Ben Embarek, a food safety expert with the World Health Organization’s Beijing office.

In recent weeks, China’s news media have reported sales of pork adulterated with the drug clenbuterol, which can cause heart palpitations; pork sold as beef after it was soaked in borax, a detergent additive; rice contaminated with cadmium, a heavy metal ; arsenic-laced soy sauce; popcorn and mushrooms treated with fluorescent bleach; bean sprouts tainted with an animal antibiotic; and wine diluted with sugared water and chemicals.

Even eggs have turned out to be man-made concoctions of chemicals, gelatin and paraffin. Producers operate in a cutthroat environment in which illegal additives are everywhere and cost-effective. Manufacturers calculate that the odds of profiting from unsafe practices far exceed the odds of getting caught, experts say. China’s explosive growth has spawned nearly half a million food producers. Fourfifths of them employ 10 or fewer workers, making oversight difficult.

China’s iron political controls ensure that no powerful consumer lobby exists to agitate for reform, press lawsuits that punish wayward producers or lobby the government to pay attention to consumer safety .

“Basically, people now feel nothing is safe to eat,” said Sang Liwei, who directs the Beijing office of the Global Food Safety Forum, a private agency. “They are really feeling very helpless.”

Increasingly well-educated Chinese are dismayed . Even top officials are discomfited.

“All of these nasty cases of foodsafety problems are enough to show that lack of integrity and moral decline have become a very serious problem,” Prime Minister Wen Jiabao told government officials in mid-April, according to The People’s Daily.

“We feel really ashamed,” Vice Premier Wang Qishan said at a meeting with legislators.

China adopted a far-reaching foodsafety law in 2009 and is bringing standards in line with international norms.

“The situation is steadily improving,” said Luo Yunbo, dean of the food sciences college at China Agricultural University in Beijing.

But the health minister, Chen Zhu, said that China had fewer than one food inspector for every 10,000 people.

Some food is simply unregulated. Pork accounts for two-thirds of the meat eaten by Chinese consumers, but only half of it goes through slaughterhouses subject to inspection, he said. The rest comes from pigs slaughtered in backyards, villages or markets and is essentially untested, he said. Oversight remains shared among disparate bureaucracies.

After the milk-powder scandal , all melamine-tainted dairy products were ordered to be destroyed. But they have turned up again and again.

Clenbuterol is another recurring problem. The drug was banned in animal feed a decade ago because it can cause heart palpitations and other problems.

But experts say it remains widely available. It is fed to pigs because it helps the animals develop more muscle and less fat and allows them to be sold for slaughter more quickly.

In April, the Shuanghui Group, one of China’s largest meat producers, recalled thousands of tons of meat and meat products after news reports that an affiliate had processed pork from pigs that were fed clenbuterol.

Consumers have also been repeatedly poisoned by excessive levels of the chemical nitrite in meat, said Feng Ping, a professor at the Beijing Academy of Food Sciences.

Unscrupulous producers also hurt reputable manufacturers. Imported dairy products nearly quintupled in 2009 , government officials say. Foreign brands now account for half of all infant milk powder sold in China.

Now steamed buns are taking a hit. A supermarket has been caught “recycling” stale buns in a filthy workshop.

The supermarket chain and other retailers that have sold the buns have blamed its supplier, the Shanghai Shenglu Food Company. The authorities have revoked the supplier’s license and have arrested five of the firm’s managers, according to Chinese news media reports.

“They really have no morals,” said a Shanghai man at the supermarket. “They will do anything for money.”