A leading Japanese businessman said yesterday that the Peoples Republic of China now presents "a great opportunity" for trade if Japanese and American businessmen cooperate in their penetration of the market instead of engaging in "undisciplined competition."

Kiichiro Kitaura, chairman of Numura Securities Co. Ltd., told a symposium here sponsored by the Nihon Keizai newspaper China is such a "colossal, untapped market" that it "can not be opened up by any one country alone."

He suggested that informal consultations between Japanese and American businessmen would be a natural way to blend Japanese and American technologies, and take advantage of Japan's proximity to the mainland of China.

Kitaura's proposal was part of his approach to a solution of Japanese-American trade problems, the main theme of the Nihon Keizai symposium. Kitaura argued that the imbalance in accounts between the two countries should not be settled by bilateral means alone, but by expansion of multilateral trade. He also spoke approvingly of the prospect of internationalizing the yen and broadening Japanese financial markets.

He agreed with a suggestion by Brookings Institution senior fellow Philip Trezise that too much of Japan's large current account (trade and services) surplus had gone into Japan's central bank reserves, and that more should be invested and loaned abroad.

Opening up the China market presents chances for both Japan and the U.S. to increase their export sales, and to help produce "a rich and stable Chinese economy (that will contribute to world economic stability," Kitaura said.

Trezise is a former State Department official with experience in Japan. He said present U.S.-Japanese relations are "stormy" and at "very high and dangerous levels." He suggested that tensions could be defused if Japan, despite its well-known fear of inflation, "converted more of its savings into (domestic) demand, stimulating imports and reducing exports."

But he said that this country should expect Japan to run sizable current account surpluses for a long time to come, which would be an acceptable policy if Japan expands its outflows of public and private capital.

Kitaura said that joint Japanese-American ventures in China are logical in steel production, offshore oil, textiles and agriculture. "And we can both extend financing opportunites, so why don't we cooperate together?" he asked.

Kitaura, Trezise and other speakers at the first day of a two-day session agreed that some progress was being made in reducing the worldwide Japanese trade surplus that had hit $24.6 billion in 1978.

But American speakers, including Peter G. Peterson, chairman of Lehman Brothers Kuhn Loeb Inc., and Rep. James R. Jones (D-Okla.), chairman of a special House subcommittee on trade, urged the Japanese to do more.

"What we need is a perception in the country and in Congress that the Japanese government and the Japanese people are willing to make trade a two-way street," said Jones.

He cited as counterproductive government officials' statements in Tokyo -- quoted in a recent Washington Post dispatch -- that the Japanese government has done all that is reasonable toward cutting the $12 billion surplus with the U.S.

Jones said that attitude will stir up already strong protectionist sentiment in Congress that threatens to become worse this year during an expected economic slowdown.

The need to alter the perception in the United States that Japan is "unfair" was brought up also by Trezise, who said that it is "simply bad advertising" when the retail price for sirloin beef in Japan is $45 a pound.

"That's distressing public relations," Trezise said. Letting more beef into Japan won't affect the trade balance much, Trezise acknowledged, but doing away with unnecessary restrictions would help the Japanese image, he said.

Echoing the case the Japaneses government has been making lately, Kitaura pointed out that appreciation of the yen had shielded a substantial improvement in the U.S.-Japan bilateral trade balance in favor of the United States.

In real (1971) terms, and with exports priced in terms of yen instead of dollars, there was an actual 4.4 percent decline in the volume of total Japanese exports in 1978, the first in 26 years, Kitaura said. Further, he predicted another decline in 1979.

Continued expansion of the domestic Japanese economy, as some have been urging, "could trigger a disastrous inflation," Kitaura said.

Nonetheless, Trezise -- although rejecting as too simplistic the argument that the Japanese surpluses can be attributed wholly to a protectionist attitude -- said that a principal reason for the trade imbalance is the sluggish recovery in Japan from the 1974-75 recession.

Even though the Japanese are running a sizable deficit -- proportionately much bigger than that of the United States -- "it is arguable that the Tokyo authorities have been too prudent in their economic policies," Trezise said.