The U.S. Army Corps of Engineers has already established a beachhead in China with President Carter's full blessing, and eventually may widen it to include taming the Yangtze River.

Corps specialists are winding up a China tour that included presenting papers at a symposium in Peking on how to build dams, dig channels and make other changes in freezing weather.

Lt. Gen. J. W. Morris, chief of the Army Engineers, said in an interview that China and other developing nations are turning increasingly, through the State Department, to the corps for help in developing their waterways.

The crops' involvement in Asia, the Middle East and Africa comes at the time when U.S. policymakers find the regular U.S. military establishment of little use in influencing events in the Third World.

Morris, declaring that he agreed with the recently expressed view of Marine Corps Commandant Louis H. Wilson that the developing nations will be in turmoil for the foreseeable future, said developing river basins an making other visible improvements would strengthen progressive governments and relieve frustrations.

In addition to China, South Korea, the Philippines, Indonesia, Saudi Arabia, Oman, Qatar, Nigeria, Gabon and Brazil are among those already discussing projects with the corps.

One reason that China and other nations were welcoming the corps these days, Morris said, is that "they know we're not going to establish a permanent presence."

"They know we're there either to transfer to them physical things," ranging from airfields through dams to shopping centers, "or transfer the expertise and knowledge we have learned" in over 200 years of engineering in the United States, Morris said.

"Our idea is to work ourselves out of a job" in those foreign countries and leave something positive behind, said the Army's chief engineer.

Although Morris stressed that the corps' overseas activities will not diminish the engineers' role at home, other specialists said the Third World is spending money for dams and other river development at the time when there is a declining demand for this kind of work in the United States.

"Look at a map of the underdeveloped world and you can see the great potential for river-basin development," said one Army engineer. He cited the Yangtze and Niger as two leading examples.

China's untamed Yangtze is sometimes 50 feet higher in summer than in winter, and flows with enough force to double the nation's electricity if harnessed to turbines.

Corps water-power specialists already have visited China to discuss possibilities. This week two civilian employes of the corps, Albert F. Wuori and Kin-Chao Yen of the cold weather laboratory in Hanover, N.H., are to present papers at a seminar in Peking on construction techniques for freezing weather.

A team of Chinese civil engineers is winding up a 54-day study of U.S. waterway projects, including 26 built by the Crops of Engineers. The Chinese, according to Army engineers, are interested in developing their inland waterways for transportation as well as for electric power.

In Nigeria, Morris said, if the agreement in its final stages is signed, "We're going to take the Niger River and develop it for commerce and make it navigable, like we've done for the Mississippi. This would be a forever kind of contribution of Nigeria's transportation capability and economic base."

Morris said the Third World countries with oil earnings to spend, like Saudi Arabia and Nigeria, seem determined to invest them in lasting improvements rather than buy flashy consumer goods.

"Almost every bit of this work that we're doing overseas is being paid for by the countries themselves," in contrast to the immediate post World War II years, when the United States paid for most of the overseas construction, Morris said.

The Army's chief engineer said that the environment movement also has spread to the Third World, partly because most of the foreign leaders inviting the corps into their countries have been educated in the United States.

"They're very sophisticated," said Morris, in declaring that environmental concerns are being addressed as the corps designs and builds in the Third World.