The World Bank, as part of its "special action" programs to help Third World nations overcome problems associated with huge debt, yesterday approved two loans for Mexico totaling $525 million, the largest amount ever approved by the Bank for Mexico at one time.

One loan, for $350 million is to Mexico's National Foreign Trade Bank to help stimulate non-oil exports. The other, for $175 million, is to Nacional Financiera S.A. (NAFINSA), the Mexican National Development Bank, to aid small and medium-ssized enterprises.

The two loans, for a 15-year period, carry an interest rate keyed to the cost of World Bank borrowings, plus a 0.75 percent commitment charge on undisbursed balances, and a front-end fee of 0.25 percent. The loans are guaranteed by the United Mexican States.

Bank President A.W. Clausen is known to feel that World Bank special assistance of this kind, stressing a nation's ability to boost its export sales, is the best way that his institution can supplement the key role of the International Monetary Fund, which is providing shorter-term balance of payments assistance.

The Bank said yesterday that the $350 million loan will help up to 725 Mexican companies, and help the Mexican nation achieve its goal of a 400 percent boost in nonpetroleum exports over the next five or six years. The $175 million package is designed to help 3,000 firms, generate 10,000 jobs and preserve up to 30,000 others over the next three years.