This evaluation report on the Green Thumb program is the first in a series of three reports that will constitute a comprehensive evaluation of Operation Mainstream (OM). Operation Mainstream is a collection of programs designed to employ as enrollees poor, chronically unemployed adults. This evaluation relies primarily on cross-sectional and before-and-after analysis to determine program impact within the sample OM communities. The report evaluates the Green Thumb-Green Light program on two levels: (1) the degree of correspondence between program goals and the congressional intent for the Mainstream program, and (2) the effectiveness of program design and operation in achieving program objectives. Recommendations are: (1) The basic strategy and emphasis of the program should be modified so that the program provides more services of direct benefit to the poor and aged, (2) Consideration should be given to the strategy of concentrating efforts and resources in order to intensify impact and to facilitate administration, (3) The advisory committee should be strengthened, (4) Supportive services should be given more effort, (5) Annual medical examinations and safety training should be insured, and (6) Procedures should be instituted to insure that enrollees understand the reasons for their termination. (GB)