C. Fred Bergsten, former chief spokesman for the Carter administration on international economic issues, warned yesterday that the dollar had moved so high on international markets that the competitiveness of American goods may once again be threatened.

Bergsten, who had been Treasury assistant secretary for international affairs, said in congressional testimony that the "mix" of the Reagan economic policies threatens to worsen this trend because it will result in tight money, driving interest rates higher and carrying the dollar upward.

Treasury Secretary Donald Regan, on the other hand, said last weekend on NBC's "Meet the Press" that he believes that the Reagan program eventually would bring interest rates down. "I think also you'll see the dollar soften a little bit," he said, "because a lot of the money that's been attracted over here has been because of our high rates of interest."

Bergsten also opposed the Reagan administration's decision to stretch out American contributions to the International Development Association, the soft-loan affiliate of the World Bank, and to slash the funding for the Export-Import Bank.

He charged that both proposals would hurt the U.S. economy by affecting U.S. exports, which have become an increasingly important component of the gross national product. He charged that the main result of cutting the Export-Import Bank budget would be loss of U.S. markets, as trade rivals such as France benefit from increased export subsidies. He predicted that the Reagan administration eventually would reverse its own policy, leading to Ex-Im Bank financing at higher levels to match the foreign programs.

On the question of currency relationships, Bergsten said in his testimony that the dollar had appreciated by 12 percent on a trade-weighted basis since November 1978 -- when the United States set out to bolster the value of the dollar -- almost fully offsetting the depreciation that occurred in 1977 and 1978.

If the dollar gets stronger than justified by the underlying economic relationships among nations, Bergsten said, American exports -- which have been growing at twice the rate of growth of world trade over the past three years -- would be set back.

The former Carter aide said bluntly that President Reagan "was incorrect" when he said in his State of the Union address that one of his goals is "to make the United States competitive once again in world markets." To the contrary, Bergsten asserted, the Reagan economic policy "could in fact undermine the currently very strong U.S. competitive position."