By John S. McClenahen Although proof must await results, some largely unpublicized agreements signed during President Clinton's weekend trip to Nigeria promise to produce significant sales for U.S. manufacturers. James A. Harmon, chairman of the U.S. Export-Import Bank (Ex-Im Bank), signed a so-called project incentive agreement with the Nigerian government and the Central Bank of Nigeria for specialized funding that's expected to increase the financing of U.S. exports destined for Nigerian infrastructure projects. The agreement includes security provisions for transactions that use hard-currency export contracts -- such as those generated by oil and gas sales. Harmon also inked master guarantee agreements entering into partnerships with four Nigerian banks: Union Bank PLC, United Bank for Africa PLC, FSB International Bank PLC, and Equity Bank of Nigeria Ltd. The arrangements allow Ex-Im Bank to guarantee the repayment of loans made by the banks to creditworthy Nigerian buyers of U.S. goods and services. Nigeria is only the second nation in sub-Saharan Africa -- the other is South Africa -- in which banks have been approved for a master agreement.