The International Finance Corp., the World Bank's private-sector arm, is embarking on a campaign to raise its public profile to fulfill its new goal of doubling its investments in the Third World over the next five years.

Under the leadership of Sir William S. Ryrie, who became executive vice president on Oct. 1, the IFC will be more aggressive in seeking out and identifying private-sector projects that will aid in the development of poorer nations, agency sources said.

The IFC also plans to explore innovative ideas on how it might participate in stimulating new private enterprise in the Third World. One plan calls for the investment of about $100 million in oil and gas exploration projects by companies below the level of the majors.

Another idea, but one still far from refinement, is to convert some portion of existing private commercial loans to equity, perhaps through the IFC acting as an intermediary.

"We have to be more energetic in making ourselves known," an IFC official said. "There are many companies interested in investing in the Third World that have never heard of us. They, of course, know of the World Bank. But we have only a small staff, while they have a large staff and high visibility."

Coincidentally, the IFC announced yesterday that, for the first time, it has borrowed $50 million in the private capital market. Normally, the IFC borrows most of its funds through the World Bank. But under the expansion program announced last June, its borrowing needs will run as much as $2.5 billion, more than three times its cash needs in the prior five years.

In a statement, Ryrie said the borrowing had been obtained on especially favorable terms -- 11.42 percent on a semiannual equivalent basis -- "and will help establish us in the banking world in a way that will be helpful."

The United States, supported by other key member governments in the World Bank Group, has been pressing bank President A. W. Clausen and his staff for a greater emphasis on the private-sector role in development, and less concentration on concessional aid through governments.

In urging new leadership at the top of the IFC, Reagan administration officials have argued that it should have been playing a bigger role in the last several years. For the past four years, under former executive vice president Hans A. Wuttke, the IFC failed to increase its dollar investments in the Third World.

In June, the executive directors announced the approval of a doubling of the IFC's capital to $1.3 billion.

Officials said that this will allow the IFC to invest a gross amount of $7.4 billion in private-sector projects worth about $30 billion in 80 developing countries over the next five years.

Officials are waiting for the subscribing countries to approve the various capital increases. The U.S. share -- $175 million, or 26 percent -- is expected to be voted by Congress by this spring.

The new capital would allow the doubling of the investment program over the past five years. But officials said that, at the moment, there may be a shortage of viable projects.

Ryrie is said to believe that the IFC, which has a professional staff of only 230 (compared with the World Bank's 2,800), needs more experts in the field, examining worthwhile private-sector projects that may be a bit too risky for the private sector unless there is the "umbrella" security of an international agency such as the IFC.

The IFC also intends to explore the possibilities of greater portfolio investment in some Third World countries and to look at the overall development needs of a given nation, rather than the more narrow boundaries of the potential success of a single project.

In pursuing its expansion goals, the IFC is under pressure to "do a lot more in Africa," a source said, but believes its loans will grow larger in all Third World sectors.

The management also believes that the private-sector role can be boosted in India, provided the new government there helps get rid of bureaucratic obstacles.