A group of 35 major multinational banks from 10 countries announced yesterday that they have formed an organization to keep track of the economic and financial conditions in major borrowing nations such as Brazil, Mexico and Argentina.

More than a score of nations--many of them in Eastern Europe and Latin America--have had difficulties repaying their large foreign borrowings, bringing the international financial system to the brink of crisis several times in the past year.

William Ogden, vice chairman of Chase Manhattan Bank, said the new organization, the Institute of International Finance, will gather information that will "fill the holes" in economic and financial statistics currently available about major borrowing countries and provide that information to banks that are members of the institute.

For example, it was not apparent on the basis of data now available that the short-term debt load at many developing countries had skyrocketed during the past 18 months, he said.

The assumption under which founding banks are operating is that, if the lenders knew more about the economic conditions and the financial burdens in the borrowing nations, these countries would not have been able to accumulate the mammoth debt loads they now have. For example, Brazil and Mexico each owe foreigners more than $80 billion.

Apparently to forestall charges that it will be anticompetitive, the institute said that member banks will not report information about their own lending practices to the multinational agency, which will be based here.

The institute will develop its own information-gathering techniques, some of them apparently in cooperation with the borrowing countries.