A conference here in genetic engineering designed to foster cooperation between Chinese and foreign scientists has ended in sharp American criticism of the work of one of the most politically well-connected scientists in China.

One American scientist, Harvard University molecular biologist Walter Gilbert, said yesterday some of the work done by Chinese-American bologist Niu Manjiang "looks like alchemy." Conference participants said critical comments about Niu's methods brought a spirited counterattack from Niu, who has close contacts in the Chinese leadership and spends much of his time guiding the work of Chinese scientists in Peking.

Other American scientists, who declined to be named, said they also disputed Niu's conclusion that it is possible to change the genetic makeup of an organism by injecting ribonucleic acid (RNA), a key element in transferring the genetic code, into the organism's eggs.

"It's Lysenkoism in China," said one U.S. participant, referring to the since discredited theories of biologist Trofim Lysenko that once held sway in the Soviet Union.

Some conference participants said they were told that some younger Chinese scientists are unhappy at being instructed to use Niu's methods and that some older Chinese scientists stayed away from the conference because of disagreement with Niu.

Attempts to reach Niu at Peking's Cell Biology Institute were not successful.

It is unclear how much Niu's method, which Gilbert and others said does not provide enough controls to test results, has affected scientific research here. However, Niu's role as a conduit between the American and Chinese scientific communities has been substantial at a time when Peking is eager for foreign help in reviving its moribund research facilities.

Scientists here say Niu helped organize the Cell Biology Institute and has provided it with much of its laboratory equipment. He is close to Vice Premier Fang Yi, China's science czar, and was instrumental in arranging that an honorary degree from Temple University, where Niu teaches, be given to Chinese leader Deng Xiaoping during Deng's 1979 visit to the United States. Gilbert and other scientists at the conference, who left Peking today to visit other parts of China, said that although foreign biologists were generally critical of Niu's method, a few thought it was possible his results could turn out to be valid. Gilbert said he and other U.S. scientists here for the first time were surprised at how far behind the Chinese were in this field. They said more advanced foreign techniques could be used to check Niu's results. "We saw a nest of Chinese doing this kind of research, extremely uncontrolled experiments, which don't prove what they say they are proving," Gilbert said.

One foreign resident of Peking who is familiar with the Chinese university system said, "Many Chinese, as well as foreigners, think of Niu as sort of a scientific huckster. But he is very active and energetic and the Chinese clearly feel he is useful to them. That institute is very well equipped, because of him."

Niu's experiments are designed to show that goldfish with one type of fins can develop fins of another type and pass them on to their offspring if RNA from fish of the second type is injected into the goldfish eggs. Gilbert said the experiment did not allow for natural genetic differences that could explain the change and needed control groups to verify the results. He said some cancer researchers in China also are attempting to treat cancer patients by injecting them with RNA. These experiments also are not carefully controlled and it is difficult to determine if improvement is the product of the RNA or another factor.

Niu's work has received a great deal of official publicity in China's as Peking has attempted to encourage scientific endeavor by publicizing the successes of Americans of Chinese ancestry.

Several Chinese-American scientists, particularly physicists, have lectured here. The only three men of Chinese decent to win Nobel prizes are all American physicists. All have been warmly received by top Chinese leaders here and encouraged to lecture to Chinese scientists.