Washington — The social security system faces problems with not having enough money to pay the nation's elderly and dependents, a study by the congressional Joint Economic Committee concluded. The report said projections show that the fund's reserve levels "will be inadequate to maintain the cash flow of the program by late 1981 or early 1982." It urged that private pension plans be encouraged to help alleviate part of the system's load, and suggested "increasing the retirement age, reducing benefits, expanding the coverage of social security to include federal employees in order to increase revenues . . . ."