Employees of the Delta Diablo Sanitation District may think twice about calling in sick if the Contra Costa County Board of Supervisors approves an incentive plan. District officials have proposed using state lottery tickets to induce the 37 employees not to call in sick if they are not. Operations Director William McDonald said that under the plan, all employees would be entered in a drawing. At the end of each month, names would be drawn until two employees who did not take sick leave that month were chosen. Each would receive $50 worth of lottery tickets. McDonald said the tickets would cost only $1,200 a year, while the district spent $19,177 in sick pay in 1985.