This study emphasizes the impact of family planning program components on contraceptive prevalence in less industrialized countries. Building on Lapham and Mauldin's "Program Effort and Fertility Decline" framework and policy evaluation's theory, the author developed two models to examine the impact of family planning programs on contraceptive prevalence and fertility under the constraints of socioeconomic development and demand for family planning. The study employed path analysis and multiple regression on data from the 1982 program effort study in 94 less developed countries (LDCs) by Lapham and Mauldin and 98 LDCs of the 1989 program effort study by Mauldin and Ross. The results of data analyses for all data sets are consistent for the most part. Major findings are as follows: (1) A combination of program effort and socioeconomic development best explains the variation of contraceptive prevalence. (2) Among socioeconomic variables, female literacy exerts the strongest direct and indirect influences to increase contraceptive prevalence and indirect influence to decrease total fertility rate. (3) Christianity performs a significant role in reducing contraceptive prevalence. (4) Among program effort components, availability and accessibility for fertility-control supplies and services have the most influence on contraceptive prevalence. (5) When controlling for demand for family planning, female literacy and Christianity have expected and significant relationships with contraceptive prevalence. Availability and accessibility to fertility-control supplies and services exerts a positive and statistically significant impact on contraceptive prevalence. Demand for family planning has a positive and statistically significant effect on program variables, availability, and contraceptive prevalence. (6) There is a strong inverse relationship between contraceptive use and fertility. Demand for family planning, program effort, and socioeconomic development influence fertility through contraceptive prevalence. The findings of this study suggest that governments in LDCs should give priorities to increasing female education and availability of contraception to effectively reduce fertility.