Treasury Secretary Michael Blumenthal said today that the Sino-Vietnamese hostilities would not effect "the establishment of a long-term economic relationship between the United States and China."

Blumenthal talked to reporters before landing here this afternoon, the first of two refueling stops en route to Peking where he will represent President Carter at formal ceremonies reopening the American Embassy on March 1. He will also initiate longrange talks on trade and other economic affairs.

The treasury secretary said he is carrying instructions given him personally by Carter Thursday afternoon to convey to "the Chinese leadership" American concern over the outbreak of war between China and Vietnam.

He listed this as one of three "assignments" for his mission, the others dealing with the framework of economic relationships, and the symbolic upgrading of the Peking-U.S. liaison office to embassy status.

The thrust of Blumenthal's remarks aboard his special Air Force plane was that the new war situation -- in the U.S. government's opinion -- does not create a setback for normalization of relations between the United States and China.

Carter has said on at least two occasions in the last several days that the United States would not become involved in conflicts between Asian powers.

Blumenthal, while turning aside almost all questions on the military implications of the China Vietnam conflict, rejected the view that the war would complicate Sino-American economic affairs.

Asked whether the war would drain away some potential for the ambitious Chinese modernization goals, Blumenthal said that "the United States has little information on that subject." Later he added: "I think we'll learn more about that, as you will, when we get to Peking."

But he again stressed that "the main thing" is to develop a bilateral economic relationship with the People's Republic, "and we don't think that goal need be or will be affected by these other things."

At Andrews Air Force Base before taking off this morning, Blumenthal told a television interviewer that there was no reason for anyone to conclude that his mission lends tacit support to the Chinese incursion into Vietnam territory.

He acknowledged -- for the first time publicly -- that there had been some discussion within the administration after the Chinese had crossed into Vietnamese territory, whether the trip would go forward.

"But it was not a discussion for a great number of hours," he said. "The situation was reviewed, and it was decided that the trip could go on as planned."

The only apparent change in earlier plans affected Michael Oksenberg, China expert on the National Security Council. Oksenberg, scheduled to accompany Blumenthal, was left behind. A treasury official explained that it was thought Oksenberg would be more valuable in Washington given the new military situation.

Blumenthal is due in Peking Saturday, where talks with Chinese government officials will run through Friday. He will then spend two days in Shanghai, and one day in Tokyo before returning home March 5.