The globalization of securities trading has created new opportunities for international fraud and has challenged regulators to protect U.S. investors without stifling overseas competition, the acting chairman of the Securities and Exchange Commission told Congress yesterday.

"The ability to move capital quickly across national boundaries and to engage in securities transactions through offshore entities provides new mechanisms for the unscrupulous to engage in securities fraud," Charles C. Cox said in testimony before the House subcommittee on telecommunications and finance.

Cox told the committee that the SEC had tried to battle international fraud by working with other governments to exchange information on insider trading cases. For example, he said, the Swiss recently allowed the United States to obtain the identity of a customer of a Swiss bank who was involved in an insider trading investigation. The United States also has information-exchange agreements with Britain and Japan, he said.

The information flows both ways, Cox told the committee. The SEC gets more requests for investigative information from overseas than it sends abroad.

Cox cited the problem of international securities fraud as one of the many issues confronting the SEC in an era when global, 24-hour securities trading is an accepted fact and when corporations and nations routinely cross each other's borders to raise capital.

"What is at issue here is the balancing necessary to coordinate our markets with the differing regulatory structures of other nations," Cox said. The job, he noted, was finding a way to make the markets work in tandem "without sacrificing investor protection."

Cox testified in connection with the delivery by the SEC of a voluminous study of the internationalization of securities markets. The study, prepared by the SEC staff, makes no specific recommendations.

Rep. Edward J. Markey (D-Mass.), the subcommittee's chairman, and other members expressed concern about the possible impact on U.S. markets of actions taking place in markets overseas.

"Are we truly ready for globalization on such a vast scale?" he asked. "What are the implications for individual markets when a major link begins to break? More pointedly, what would be the effect on the Dow {industrial average}, presently above the 2500 mark, if the Nikkei {Japanese} market index, presently hovering hear the 25,000 level, began a significant decline?"

Markey directed the question to Cox, but Cox said in effect that there was no easy answer.

The explosive increase in international trading and financing was reflected in SEC figures that showed the following:

The total of international bonds issued in 1980 was $38 billion. In 1987, it was $225 billion, with $44 billion came from U.S. investors.

U.S. investors bought and sold $102 billion in foreign stocks last year. Foreign investors bought and sold about $277 billion in U.S. stocks.

The United States has been lagging other countries in the growth of the value of its equities. Between 1978 and 1986, the value of Japanese stocks grew on average at an annual rate of 23 percent, Italy's at 39 percent, Great Britain's at 18 percent and the United States' at 14 percent.