BEIJING — China is facing a storm of protest at home and abroad over new regulations requiring all personal computers sold in the country to include software that can filter out pornography and other “vulgar” content from the Internet.

Industry executives, free-speech advocates and ordinary computer users have responded angrily to the new mandate, which gives manufacturers until July 1 to preinstall the software on millions of new machines. The government presented the regulations to PC makers on May 19, but they were not released publicly until Monday.

Computer makers in the United States say it will be impossible to fulfill the requirement by the end of the month and have asked the Chinese government to reconsider the directive. They say it raises thorny questions about censorship and whether manufacturers will be liable if the software — designed by a company with ties to China’s military and public security agencies — conflicts with operating systems or causes computers to crash.

“To be honest, nobody really knows what this software is capable of,” said one executive at an American computer maker.

So far, the government has not shown any signs of backing down. On Tuesday, state-owned media and officials defended the new software, known as “Green Dam,” and said concerns that it could be turned into government-operated spyware were exaggerated.

“If you have children or are expecting a child you could understand the concerns of parents over unhealthy online content,” Qin Gang, a Foreign Ministry spokesman, said at a regular news conference Tuesday.

Independent-minded newspapers and Web sites have greeted the announcement with skepticism, questioning the software’s reliability and wondering whether it could be used to censor nonsexual content. Others criticized the government’s decision to spend 41 million yuan, or $6 million, on the program. China has shut down thousands of pornographic Web sites this year and regularly uses other technology to block other sites devoted to Tibetan independence, human rights issues and other politically sensitive subjects.

“How do you prevent this from becoming a backdoor for the misuse of power?” asked an editorial on the Web site of Caijing magazine. “Up until now, officials have not answered these questions. The government can urge parents to take responsibility through a variety of mechanisms, but it can’t become an omnipotent Big Parent.”

Green Dam’s designer says the program is not capable of acting as spyware and can be disabled by computer owners who don’t want to use it.

The Beijing News devoted a full page to Green Dam, which uses image recognition technology and text filtering to block material. The newspaper said that tests of the software, which has already been installed in thousands schools, found Green Dam’s performance less than stellar. For example, an innocent math question that included the word “balls” was filtered out, as were harmless photographs with yellow and black backgrounds.

Writing on Green Dam’s own Web site, one teacher said sexually explicit images slipped through and another complained that it would not let her view pictures of pigs. “Pitiful little pig!” she wrote. “I was curious, so I looked up some photos of naked African women. Oh, they were not censored!”

Wang Xiaofeng, a popular blogger, said a friend who downloaded the software was unable to view his satirical writings. He said he is especially bothered by the way Green Dam has been introduced to, or rather, foisted on, the public.

“It’s like a bully forcing people to do what they want,” he said in a telephone interview. “Whether their intentions are good or sinister, the government carried this out in a bad way.”

Computer makers, who last year sold about 40 million PC’s in China, would agree with such sentiments, although none were willing to speak on the record for fear of angering a government they hope will change its mind.

Manufacturers and software designers have been working behind the scenes to convince officials to reconsider the directive, which was drawn up without industry input and without warning.

On Tuesday, a coalition of U.S. trade associations issued a statement that gently made their case.

“We believe there should be an open and healthy dialogue on how parental control software can be offered in the market in ways that ensure privacy, system reliability, freedom of expression, the free flow of information, security and user choice,” read the statement, which was signed by groups including the Software & Information Industry Association and the Information Technology Industry Council, whose members include Lenovo, Dell, Apple and Hewlett-Packard.

By Wednesday, industry officials said a dialogue had begun and the American computer executive, speaking anonymously, said he had hopes that the rules might be eased.

Still, he said one possible compromise — allowing PC manufacturers to simply drop a Green Dam disc into the box of every new computer — would not be ideal. Preliminary tests by software technicians at a number of companies, he said, have revealed significant software tics that could affect a computer’s operating system or other programs.