The International Finance Corp., the World Bank's private-sector arm, has made its first investment in China -- for the production of Peugeot pickup trucks -- in a deal that will let workers buy stock in the operation, the IFC's new head said yesterday.

Sir William Ryrie, IFC executive vice president, mentioned the China project in reporting that the IFC's lending operations were back on "a high-growth track" in the fiscal year just ended, up 35 percent over 1984, with prospects good for further expansion this coming year.

Ryrie said that opportunities for private investment in the Third World were improving, and that the economic climate among the developing nations is "looking somewhat better," although no dramatic upturn is in evidence. He noted that there is no backlash against private investment in India, despite the Union Carbide disaster at Bhopal, and that private-sector growth is being encouraged by Pakistan and Bangladesh.

He said that economic prospects in Asia "are looking quite bullish"; that debt problems in Latin America are being met with help from government agencies and banks; and that "some progress" is being made in many African countries. The IFC has been able to resume its activities in both Zaire and Ghana, he said, in part because those countries are following more realistic -- and floating -- exchange rates.

Ryrie credited the IFC staff for its ingenuity in developing lending innovations and services that helped boost the agency's new investments for fiscal 1985 to a record $937 million after several relatively flat years. The earlier slow pace of IFC activity helped prompt a change in the IFC management last October, when Ryrie succeeded Hans A. Wuttke.

Net income for fiscal 1985, "even after prudent provisions for reserves against losses," increased 8 percent to $28.3 million, the IFC said.

The IFC invested that $937 million in 38 countries, and the funds acted as a catalyst for a total investment of about $3 billion, including money put up by the IFC's private partners. Ryrie said that he expected the IFC to invest $1 billion to $1.2 billion this year, which will spur overall investment of about $4 billion.

The IFC's longer-term goals include doubling the size of its operations over the next five years. This, however, depends on a doubling of the IFC's capital base, from $650 million to $1.3 billion. In turn, this proposal is dependent on approval by Congress, because the United States holds 25.5 percent of the IFC votes. So far, member countries with 71 percent of the votes have voted for the increase; a 75 percent vote is needed to make the change effective.

Ryrie said, "I am absolutely confident that we shall get that vote from Congress early in the next fiscal year."

Ryrie disclosed that the IFC, having for the first time decided to raise money on its own in private markets, was able to borrow at one-quarter to one-half percentage point less than at the World Bank, the main source of its money. The IFC privately borrowed the equivalent of $130 million in dollars and deutsche marks on a 10-year term. The agency expects to continue that pattern this year.

Among the other innovations he cited were variable-rate lending by the IFC and the use of guarantees. The agency also acted as lead manager for a $50 million underwriting (for a Latin American export bank), and proposed a new lending facility to help private-sector projects in Africa.

Other steps the IFC has taken to cast off its former stodgy image include the investment in China; an oil exploration project in Colombia; a gold exploration project in Thailand; and a life insurance company project in Indonesia.

The pickup-truck venture in China will assist a $79.5 million business operation jointly financed by French and Chinese sponsors to produce 15,000 pickup trucks a year. IFC is lending $15 million, and taking a $2.02 million equity position in Guangzhou Peugeot Automobile Co. Ltd.

Another investor in the project, China's Guangzhou Automobile Manufactory (a bus assembler), has agreed in principle to sell 10 percent of its shares to the Chinese public -- preferably workers at the Guangzhou Peugeot plant -- within two years after startup, scheduled for 1988. Other partners are the China International Trust and Investment Corp., and Bank Nationale de Paris.

Ryrie said IFC is negotiating with the government of China for other projects to help mobilize foreign capital in China. He would not identify the prospective projects.