The Asian Development Bank said in its annual report published today that it will begin a modest program of loans to private businesses in low-income countries without requiring guarantees from their governments.

The ADB, a multilateral development bank, said this new emphasis -- which ties in with a basic theme of the debt initiative announced last year by Treasury Secretary James A. Baker III -- "reflects a growing interest in the developing member countries in stimulating private enterprise. The economies of the region are becoming more market-oriented, and are placing greater emphasis on the private sector."

The Baker debt initiative, outlined last October, calls for an increase of $9 billion in lending by the multilateral banks and of $20 billion by commercial banks during the next three years to major Third World debtors -- mostly, but not exclusively, in Latin America -- provided the borrowing countries reorient their economies more to the private sector.

The ADB, which serves 32 developing and newly industrialized countries in the Asia-Pacific region, will hold its 19th annual meeting in Manila this week. It is owned by these governments, and 15 industrialized countries from Europe and North America -- including the United States -- which help finance it.

The board of governors decided last year to increase its support of the private sector among its developing country members, including private commercial enterprises and public enterprises that might become private.

The ADB's report said that, within its own area, economies as diverse as Bangladesh, India, the Republic of Korea, Malaysia, Pakistan, Sri Lanka and Thailand recently have begun to encourage private initiative. Among the motivations are the demonstrated success of countries that have promoted private enterprise and "the growing recognition of the costs of ineffective public enterprise," the report said.

The bank said that in the past, it had loaned about $2 billion to member countries for private-sector projects in industry and agriculture, of which $1.4 billion went to small and medium-scale enterprises.

It said its future approach will be broader in scope, in an effort to persuade its member countries that their "commercial enterprises, both public and private, should become more market-oriented, rather than remain protected by high import tariffs or saddled with avoidable social costs as a result of government regulation and intervention."

Until now, the ADB has required the government either to be the borrower or the guarantor for its loans, a policy that has limited its aid to the private sector.

Under the new policy of making loans to private companies even when there is no government guarantee, the ADB plans an initial commitment of $75 million out of regular funds, plus $25 million in subsidized funds during the first two years. Individual loans are expected to range from $5 million to $30 million. The bank assistance would be intended to cover up to 25 percent of the cost of an individual project.

The report also said that the ADB is prepared to provide the member countries themselves with policy and technical assistance if the country has made a political commitment to privatize public enterprises.

For all of its activity during 1985, the ADB said that lending commitments had slipped 14.6 percent under the 1984 loan total of $2.2 billion to $1.9 billion, reflecting slower world economic growth.

It saw only "modest improvement" for this year, with the collapse of oil prices cutting both ways among its member countries.

Nonetheless, the report predicted a resumption of the growth in its commitments, especially if the member countries respond to what it said would be the ADB's emphasis "on the importance of economic efficiency."