When young Cheng Shaochiung studied veterinary medicine in the United States from 1925 to 1938, malnutrition was widespread in his native China, and famines or harvest failures were a constant threat.

Chinese farming and food production have made enormous progress since then, but the agriculture practices of the world's most populous country still are primitive by the standards of industrial nations.

That is why Cheng, absent from the United States for 51 years, was in Nebraska this month, touring research laboratories, taking notes, poking his head into specially sanitized hog pens, eating in rural cafes and surprising his American hosts with his only slightly rusty English.

Cheng, who received a science degree from Iowa State in 1926 and a doctorate from Johns Hopkins two years later, is deputy president of the Chinese Academy of Agricultural Sciences. Since July 2 he and a team of animal health experts have been on a 26-day tour of the United States that signals broad changes in Chinese economic priorities, and possibly good news for U.S. grain farmers.

According to Cheng, Peking is strongly committed to shifting from dependence on a food production system relying almost entirely on a vast manpower pool and toward a modern livestock industry that will depend on some of the scientific and agricultural techniques practiced in the United States.

At least indirectly, the U.S. government has an interest in encouraging such a development since it could result in increased U.S. grain exports to feed Chinese hogs and poultry.

On a tour that has included Washington, D.C., DeKalb, Ill.; Ames, Iowa; Des Moines and Lincoln, Neb., the visitors have been catching up with techniques for breeding, slaughtering and safeguarding the health of livestock - techniques developed here during China's isolation in the 1950s and 1960s.

"Everything is new to us from the standpoint of scientific work," said Cheng, who also remarked on the vast changes that have occurred since he was here in the 1920s: larger farms, fewer farmers and increased enrollment at the veterinary schools of agriculture colleges.

During two days spent in and around Lincoln, the emphasis was on hogs, which Cheng said will have a central role in China's plans to improve its national diet.

There are 300 million hogs in China, compared with fewer than 80 million in the United States, but Americans eat more pork per person, and hog production in the two countries is a study in contrasts.

For most Chinese, pork is a delicacy eaten mainly on special occasions such as New Year's Modern hog "factories" capable of raising and slaughtering thousands a year opened recently near Peking, Shanghai and Canton. But most hogs are raised by individual farmers on small, private plots. These animals produce manure for vegetable gardens and live off weeds, household garbage, rice gruel or bran before being tied to wheelbarrow or to bicycle handlebars and taken to the butcher.

In rural areas, Cheng said, sick or injured hogs often are treated with herbs or acpuncture rather than with antibiotics and drugs, both of which are commonly used here.

American hogs confined to stalls often reach full weight in five months, less than half the time it takes Chinese pigs to do so. But the U.S. system relies on massive amounts of grain - up to 800 pounds for a single animal - as well as on elaborate methods for controlling the diseases that are a special problem in raising hogs in close quarters.

In Nebraska, the Chinese were given a look at a special technique for raising hogs in a disease-free environment.

Prof. Norman Underdahl, of the University of Nebraska's Institute of Agriculture and Natural Resources, showed the visitors how a litter of hogs is taken by caesarean section from the sow and put into a contamination-free plastic bubble.

Next day, Cheng and his colleagues traveled here to the farm of Willard Waldo, one of the state's largest raisers of disease-free Duroc breeding hogs. The visitors donned special plastic boots to prevent them from contaminating Waldo's herds. Waldo said these extreme measures have kept such killers as pseudo-rabies at bay and have prevented mange and lice from infiltrating his herds.

Despite these advances, Cheng said that some 1,000 U.S. hogs imported by China for breeding purposes in the last several years have had problems with disease. "We imported lots of Durocs in the 1930s without any difficulties," said Cheng. "We don't know what the reasons for these problems are."

In addition to this visit's practical importance to the Chinese, it also symbolizes continued relaxation between the two countries. This was evident in the friendly, professional tone of this visit, which contrasted with the stilted formality that frequently has characterized similar Soviet official visits.

The visit stems from an agreement on agricultural exchanges reache(year between Washington and Peking.

The Chinese "connection" to the United States was evident Thursday night when the visitors were gursts at a 14-course meal at the Peking Gardens, a Chinese restaurant in Lincoln. The hosts were officials of Norden Laboratories, manufacturer of animal vaccines. During the meal, the Chinese chatted with one of the waiters, a student from Taiwan.

Following the visit to Waldo's farm on Friday, the Chinese sampled a different kind of cooking - the pork chops and peppermint ice cream of Bill and Nancy's Pub and Skillet, a farmers' hangout in DeWitt. Fortified with the food, the visitors cheered and laughed as they mastered "foosball" - a table game in which "players" are maneuvered by moving metal rods.

When the game between the Chinese and some of the Americans accompanying them ended after 10 hectic minutes, nobody was sure which country had won, but it didn't seem to matter. CAPTION: Picture, Cheng Shaochiung, left, 1920s graduate of two American universities, translates for colleagues as Dr. Norman Underdahl explains lab techniques at Nebraska U. AP