The war between China and Vietnam has not deterred Chinese leaders from their concentration on the "four modernizations" of their country, Treasury Secretary W. Michael Blumenthal has told Japanese Prime Minister Masayoshi Ohira.

Blumenthal returned to Washington last night after a 24-hour visit to Tokyo where he exchanged views with Ohira on the secretary's visit to China of last week and on economic relations between the United States and Japan.

Blumenthal said his 11-day trip had been pronounced "a great success" by White House officials.

Briefing reporters on the flight from Tokyo to Washington, Blumenthal said the Japanese wondered if the Chinese were "still committed" to the economic expansion program because of the war.

Blumenthal said he told Ohira that he "saw no evidence of change of heart or determination either because of the events in Southeast Asia or for any other reason." The allusion to another "reason" is Japanese concern over what is being described in Tokyo as cancellation by the Chinese of about $2.5 billion in orders placed in Japan.

Blumenthal told Ohira he believed the Chinese were not interested in cancelling their orders but in renegotiating terms and conditions.

Informed sources say that the Chinese want Japan's credits advanced to them in dollars in expectation that in the short run Japanese currency might appreciate. But the Japanese are still insisting on Repayment in yen.

The Chinese also reportedly are seeking lower interest rates on their Japanese borrowings. But Blumenthal and the Japanese officials agreed yesterday that there should be general adherence to what is known as "the Paris agreement," which bars discounted credit terms, sometimes called "credit dumping."

Blumenthal said that he and the Japanese officials agreed that the Chinese modernization "is obviously a very ambitious one, with problems to overcome, and that only gradual progress can be made."

Blumenthal, elated with the commitment by China to pay the United States $80.5 million by 1984 to settle outstanding U.S. claims against China, nonetheless estimated that the next steps in the process, including a U.S.-China trade agreement, "will take the better part of 1979."

State Department officials said the next move will be an exchange of drafts of a proposed trade treaty. Then, Secretary of Commerce Juanita Kreps will continue the talks during a visit to Peking in May. Chinese Finance Minister Zhang Jingfu (Chang Ching-fu) yesterday accepted an invitation to visit the United States in June or july.

On the U.S. Japanese problem, which relates almost exclusively to the vast Japanese trade surplus, Blumenthal said there were "no new commitments" by Japan to reduce its surplus or to pump up its domestic economy.

But Blumenthal stressed that he and Ohira had not engaged in a negotiation, but merely an exchange of views.