A bill that would let many Defense Department civilians retire early with a 10 percent pension bonus is slowly picking up supporters on Capitol Hill.

The plan, sponsored by Rep. Barbara Boxer (D-Calif.), would give a five-year pension credit sweetener to Army, Navy and Air Force civilian workers at bases and installations facing cutbacks. Workers could add five years to their age and service time if they agreed to retire immediately. That would make many younger, less senior employees eligible to retire. For those already eligible, it would mean a 10 percent lifetime increase in their annuity.

Boxer's bill was originally designed for civilians at the Navy's Mare Island facility in California. About 2,000 of its 9,200 civilians are slated to lose their jobs because of a reduced workload. Nine Democrats -- mostly from the West Coast and South -- also sponsored Boxer's bill.

As Defense civilians in other areas learn of the bill, more legislators, including some local ones, are rushing to support it.

The newest sponsors of the Boxer bill include Reps. Stan Parris (R-Va.) and Roy Dyson (D-Md.) as well as Edward Roybal (D-Calif.),

Jim Chapman (D-Tex.),

Albert Bustamante (D-Tex.),

Martin Lancaster (D-N.C.)

and Ronnie Flippo (D-Ala.). Early Retirement Study

The government is about to take its first serious look at the pros and cons of an early retirement offer to senior staff members. With many agencies facing cutbacks, officials are looking at the cost/benefits of early retirement as a way to trim payroll costs while protecting the jobs of younger workers. For a detailed look at the early-out situation, check this space Sunday. Lump-Sum Planning

More than 200,000 retirees have taken lump-sum pension payments since 1987. The payments are an amount equal to the retirees' own pension plan contributions. Most of a lump-sum payment is taxable, and taking it reduces the lifetime pension. Still, about 70 percent of all retirees opt for the lump-sum payment, even though experts say it is a bad move for many people. Tomorrow at noon on WNTR radio (1050 AM), financial planner David S. Dondero talks about the financial and investment considerations that people should study before they take the money. Military Pay Rumor

The Retired Officers Association warns that a false back-pay rumor has resurfaced. The fake report says that military personnel serving from late 1972 until January 1973 are due back pay because of a court order. There was a court fight over President Nixon's attempt to delay federal and military raises in late 1972. The National Treasury Employees Union won a decision that said the pay delay was improper. But that issue is long gone. There is no back pay due anyone now, the association advises. Magazine, Editor Honored

Government Executive magazine and editor-publisher Timothy B. Clark have been honored by the Capital Chapter of the American Society for Public Administration. The awards cite the magazine for its in-depth coverage of the federal establishment.