A quasi-governmental agency created to insure U.S. companies against expropriation and other political risks abroad has tended mainly to serve a very small number of huge corporations, the General Accounting Office said yesterday.

In spite of a 3-year-old order from Congress that the Overseas Private Investment Corp. broaden its coverage to serve smaller businesses, last year 29 per cent of the insurance written by OPIC went to three multinational corporations, and 41 per cent went to 11.

In addition, nearly two-thirds of the dollar volume of OPIC insurance has become concentrated in seven countries - Brazil, the Philippines, South Korea, Indonesia, Taiwan, the Dominican Republic and Yugoslavia - a Senate Foreign Relations subcommittee was told.

All of these countries are governed by authoritarian regimes, OPIC critics have noted.

The three corporations with 29 per cent of OPIC insurance are Dow Chemical, W. R. Grace and J. P. Morgan. The others in the top 11 are Celanese, General Telephone & Electronics, Getty Oil, Bank of America, Standard Oil of Indiana, Weyerhaeuser, ITT and RCA.

Sen. Frank Church (D-Idaho), chairman of the Foreign Assistant Subcommittee, said that OPIC, despite its promises, has failed to slow, much less reverse, the trend toward monopolization of the $6.2 billion program.

"Doesn't this cast doubt on the whole rationale and purpose of the program - to provide incentive to invest in countries that normally wouldn't be selected?" Church asked.

"Most of the insurance continues to go to the countries most able to attract investments . . . and to the biggest companies," he added.

Both Church and J. Kenneth Fasick, director of the General Accounting Office's International Division, which studied OPIC operations, suggested that the government's dilemma may have been partially self-induced.

In 1974, Congress mandated that OPIC insurance be gradually taken over by the private insurance sector, with a 1980 deadline for complete talkoven. Last yaar, only six of 206 insurance companies invited decided to join the 15 companies already participating, but most that did seemed willing to insure industry only in the countries with the least political risk, the GAO said.

"I would have to ask whether the introduction of private insurance companies has been one of the reasons these trends have moved in the opposite direction we had hope for," Church said.

OPIC insures foreign investments against loss by exproporiation, inconvertibility of currency and by war, revolution and insurrection. It backs the indemnity with the "full faith and credit" of the U.S. Treasury.

By doing so, it can provide U.S. businesses with insurance at fraction of what it would cost otherwise. Also, the few insurance firms that offer such protection, including Lloyds of London, generally limit coverage to one year and increased premiums as political conditions change.

Foreign investments covered by OPIC now total over $6.2 billion, and revenue last year mainly from premiums paid by insured companies - was $53.7 million. Since 1966 the program has paid or guaranteed $336 million in 61 claims, including $11 million in cash payouts.

The GAO's Fasick testified yesterday that Congress, in view of OPIC's failure to increase private insurance company participation, should consider four options: stretch the deadline beyond 1980, lower the goal of 100 per cent private involvement, abandon attempts to involve the private sector, or simply disolve OPIC.

William C. Goodfellow, deputy director of the Center for International Policy a Fund for Peace policy Study group called OPIC" primarily a service to U.S. multinational corporations who are the principal beneficiaries of its programs."

Goodfellow charged that the insured investments included game lodges built by Avis Corp. and TWA Hilton International, and luxury hotels by Pan Am Intercontinental Hotels Corp., projects he said heightened foreign resentment of the United States and did little to advance social conditions in the countries involved.

LeRoy J. Simon, chairman of the Overseas Investment Insurance Group, the consortium of private insurers, challenged the assertions of monopolization trend, saying, "While it perhaps is socially desireable to include small companies, the insurance companies are indifferent to who they insure."

Also, he said, the insurers were not concerned about the riskiness of the least developed countries, but simply were providing service where the U.S. industrial firms decided to locate.

In fact, Simon said, the insurers were concerned about the concentration of OPIC clients in a few countries because, "the more eggs in one basket that exist, the riskier the entire portfolio of business becomes."