When Nancy Reagan and Lucia Pinochet had tea at the White House yesterday, one subject that seemed unlikely to come up was whether or not the Reagan administration will certify Chile's eligibility to receive military aid from the United States.

Chilean President Augusto Pinochet is trying to clean up his country's image on human rights to qualify for that aid -- a decision the Reagan administration reportedly delayed until after last week's election.

Just a few days ago, Pinochet announced the creation of a "high-level commission" to determine whether Chilean exiles will be allowed back into that country. There are an estimated 40,000 political exiles and several hundred thousand others, according to the Council on Hemispheric Affairs, an independent organization.

Some see Lucia Pinochet's visit here as part of that public relations effort. This week, she will visit Children's Hospital and the Capital Children's Museum. She will also preside at the opening of Galeria Chile, a Wisconsin Avenue sales gallery of Chilean handicrafts being marketed under the auspices of the Chilean Mothers Foundation (CEMA), of which she is president. Another such gallery is scheduled to open in New York.

"A courtesy tea" is how Sheila Tate, Nancy Reagan's press secretary, described the first lady's hospitality for the Chilean visitor. Also attending were Gaetana Enders, the wife of the assistant secretary of state for Inter-American Affairs, and Mrs. Enrique Valenzuela, the wife of the Chilean ambassador. Mrs. Reagan and Mrs. Pinochet reportedly talked about the first lady's involvement in the Foster Grandparents Program and her Chilean counterpart's work with special children.