The Export-Import Bank will provide discount loan support for a sale to Colombia of $300,000 of solar equipment manufactured by Solarex Corp. of Rockville.

The bank will provide the discount loan to Maryland National Bank at an annual interest rate of 12 percent. Maryland National will lend the funds at 13 percent interest to a Colombian utility company, which will purchase solar panels, regulators, mounting structures and batteries from Solarex. The equipment is intended for use in a rural telecommunications system.

Jose A. Trujillo, Solarex regional sales manager for Latin America and Asia, said the Export-Import Bank loan guarantee is the first for the 10-year-old solar products manufacturer, even though the firm does half of its business overseas. Solarex has, however, worked with the Inter-American Development bank on a project in Costa Rica.

Trujillo said many of the company's sales are in less developed countries because power distribution often is less advanced in such locations, providing fewer obstacles for alternative energy.

Robert Waite, vice president for public affairs of the Export-Import Bank, said the Solarex sale is indicative of attempts by the bank's staff to be "less boiler and railroad oriented" and to focus more on U.S. suppliers involved in alternative energy and high technology.

Suppliers from France, West Germany and Japan also competed for the contract, Waite said.

Recent agreements by international lending and financial institutions: Inter-American Development Bank

* A $500,000 financing to Costa Rica to provide credit for small agricultural fisheries and agro-industrial projects.

* A $36 million loan to Ecuador to help carry out feasibility studies of three hydroelectric projects.

* A $9.75 million loan to Costa Rica to carry out a municipal investment program to include construction and maintenance of roads, sewers, slaughterhouses, community centers and waste collection and disposal centers.

A public offering of 100 million Swiss francs of its 10-year bonds in Switzerland. The issue is equal to approximately $45 million. World Bank

* A Eurodollar borrowing of $200 million of 10 7/8 percent, seven-year notes of 1983, due Jan. 13, 1990, and $100 million of 11 1/8 15-year bonds of 1983, due Jan. 13, 1998. The issues were offered at par and are non-callable. International Monetary Fund

* A standby arrangement for Thailand, authorizing purchases up to the equivalent of 271.5 million special drawing rights over the period ending Dec. 31, 1983. The financing is from the IMF's ordinary resources. Export-Import Bank

* A guarantee of a $3.4 million private loan to assist in the purchase of $14 million in canning equipment and services by a Colombian company. American suppliers include Reynolds Metals Co. of Richmond and Continental Shellmar of Puerto Rico, which is the export division of Continental Can Co.