President Reagan's appointee as under secretary of state for economic affairs told Congress yesterday that "foreign economics is more and more the stuff of foreign policy" and that the State Department would therefore take a lead role in shaping U.S. positions on international economic issues.

"After three months sitting there [as under secretary-designate]," Myer Rashish told his confirmation hearing before the Senate Foreign Relations Committee, "I'm even less willing to distinguish between economic and political considerations in foreign policy that I was before. It's a brave man who tries to draw the line."

Rashish said that Reagan's foreign economic policy would be free-market oriented, providing "an increasing role for the private sector." But he said it would not try to duplicate the efforts of some nations, such as Japan, that heavily subsidize private activity in foreign markets.

Robert Hormats, nominated to be assistant secretary of state for economic and business affairs, told the committee that top priorities in the international economic arena would include a strong effort to promote exports and to eradicate a belief held heretofore that "the State Department is not a friend of business."

Sen. Jesse Helms (R-N.C.), who has placed "reservations" on the approval of several State Department appointees, failed to appear at the hearing, having been detained in North Carolina making speeches in support of the president's economic program.

Whether Helms will get a chance to question Rashish remains unclear. After the hearing ended, committee Chairman Charles H. Percy (R-Ill.) told The Washington Post he sees "no reason to have another hearing. The record is clear, and Rashish is well known. We need to move these nominations along to a vote as quickly as possible.

But Helms delivered a letter to Percy last night saying he would submit written questions for both Rashish and Hormats, and if not satisfied with their answers, would like an additional day of public hearings. Percy said he would poll the committee and move for a vote on Tuesday unless other members join Helms' request.

In responses to questions from Percy, Sen. Nancy Kassebaum (R-Kan.) and Sen. Bill Bradley (D-N.J.) -- who appeared as a guest of the committee -- Rashish made the following points:

The administration is against admitting the Palestine Liberation Organization to observer status in the World Bank and International Monetary Fund. "I can see no purpose to it, and I am adamantly against it," Rashish said.

Contrary to published reports, "no decision has yet been made whether to lift or not lift the grain embargo.

The administration is not "indifferent," as some have charged, to poverty and other problems in the Third World.

The State Department will play an active role in formulating an international energy policy but, as in all other relationships, will strive for a "collegial" rather thana competitive role with the Department of Energy and other agencies.

The economic summit in Ottawa in July will discuss several key energy issues, including stockpiling of oil and ways to curtail imports. Rashish, if confirmed, will also assume the role of the president's personal representative for economic summits, an ambassadorial post held in the last administration by Henry Owen.