President Carter gave world financial leaders an upbeat assessment yesterday of U.S. economic prospects for next year, promising "vigorous and non-inflationary growth" and declaring, "I am committed to make sure that optimistic prediction comes true."

In a brief address to the Joint Annual Meeting of the World Bank and International Monetary Fund, which began yesterday, Carter was obviously mindful of concern over sagging worldwide economc growth evidenced at preliminary sessions over the weekend. World financial leaders, fearful of high and growing unemployment, had decided at the policymaking session of the IMF Interim Committee on a subtle shift in strategy to encourage faster growth in many large nations. Seemingly in accord, Carter invited all countries to "pursue economic growth along with us."

Carter, who voiced warm praise for the efforts of both the bank and IMF, was warmly received in turn by an audience of nearly 4,000, including 3,000 delegates, in the Sheraton-Park ballroom.

He said the two main economic challenges facing world leaders are "to restore and maintain the steady, non-inflationary expansion of the world economy, and to increase the pace of growth in the developing nations of the world."

The President said the United States would meet its target of 6 per cent growth for this year. That is a reference to the expected fourth-quarter 1977 level of economic activity compared with fourth-quarter 1976. For 1977 as a whole. Carter's economists talk of a 5 per cent gain over 1976.

He also said "the unemployment rate is going down steadily," which he said "bodes well for the future." Actually, the jobless rate rose from 6.9 per cent in July to 7.1 per cent in August, but is below its 1975 recession peak of 9 per cent.

Carter went out of his way to endorse new initiatives by IMF managing director H.J. Witteveen and bank president Robert S. McNamara.

He said Witteveen's establishment of a new special $10 billion fund to help meet balance-of-payments deficits "has my country's full support."

And he expressed "hope that a negotiation for a major general capital increase for the World Bank will permit the bank to increase its real lending." This is a turnaround from the position of the Ford administration, which barred a general capital increase sought by McNamara.

Meanwhile in their own keynote addresses to the joint meeting yesterday morning, McNamara and Witteveen joined in the call for acceleration of the growth rate in the industrial world.

Witteveen noted that previously IMF had told governments that - because of the danger of inflation - they "should not shade policy risks on the side of growth." But because growth has lagged so far below what is necessary, he said the new instruction is that the "lag in demand growth should now be decisively corrected."

A high U.S. Treasury official cautioned reporters that neither IMF nor any of the finance ministers is issuing a general call for "reflation," but merely intending to put "increasing pressure on those who can reflate and should do so," such as West Germany and Japan. He emphasized a U.S. concern that countries like Great Britain, France and Italy might "get into trouble again" if they start an expansionary process too soon.

McNamara said, "We must design a development strategy that can both accelerate economic growth, and channel more of the benefits of that growth toward meeting the needs of the absolute poor." He also called for a vast expansion of rich-country imports of manufactured goods from poor countries.

Witteven made explicit the Saturday conclusion of IMF's policymaking Interim Committee that "the faltering" of the pace of recovery calls for new economic stimulus. He said "any major reduction in unemployment levels" can come only "from markedly higher rates of economic expansion."

Without directly mentioning the United States and France, Witteveen observed that protectionist sentiment is rising, with a weakening in the commitment of some countries to a system of international trade free from restrictions and discrimination."

One sign of this, Witteveen said, is "selective restrictions on imports." He was referring to the "orderly marketing agreements" by which the United States is limiting imports of color television sets and cheap shoes from Asian countries.

Another evidence of growing protectionism, according to Witteveen, is "the interest being expressed in the orgainzation of markets," which would put multilateral limits on the growth of exports and imports.

The better strategy, Witteveen said, lies in trade negotiations under way at Geneva that could provide fresh impetus to trade expansion, and in achievement of a rate of economic growth "sufficient to permit a gradual reduction in unemployment."

He called on all countries "in a relatively strong position" to maintain an adequate growth rate in their domestic economies Witteveen finessed the question of whether the United States needs to increase its present rate of growth, saying that U.S. expansion should be "maintained at a satisfactory rate."

IMF relies on official U.S. assurances that the growth rate will be around 5 per cent over the next 18 months. But many economists, including those working for the Joint Economic Committee in Congress and the Congressional Budget Office, think that without further stimulus the actual result may be closer to 4 per cent. Privately, IMF analysts think a U.S. growth rate that low would have serious implications for the world economy.

The pressure on Japan to reduce its expected $9 billion current-account surplus this year, as reported in yesterday's Washington Post, was maintained in continuing conversations yesterday among the major powers.

But in addressing the joint session. Japanese Finance Minister Hideo Boh ignored these demands, saying only that "we will explore" efforts to promote imports.