AN UNSTATED QUESTION links these two books. Can this country afford the congeries of overlapping retirement plans-- private, public, military, veterans' and social security-- that have been established?

Since the Depression '30s, we have built a hodge-podge of retirement protection. The benefits paid take approximately one-eighth of each year's national income. The annual cost has tripled during the 1970s; the national income has only doubled.

Alice Munnell's Pensions for Public Employees sums up what should be generally known about one segment of this miscellany. A total of 6,700 government-- federal, state and local-- retirement plans cover 22 million individuals. The annual cost to taxpayers-- over and above contributions by employes-- is in the billions.

These plans pose three major problems. They permit workers to retire at unduly low ages-- at 55 and even 40 years of age. Many are inadequately financed; there is no assurance (in conventional actuarial terms) that benefits can be paid in the future. For example, the Federal Civil Service Retirement Funds, according to the Comptroller General, has an unfunded future liability of more than $120 billion. And these public plans are poorly coordinated, with other plans and with the social security system. Hence, some employes who move from job to job end up with inadequate pensions and others enjoy unwarranted multiple protection.

A President's Commission on Pension Policy has been created to recommend solutions. The history of recent decades, however, offers little promise that this commission will "bite the bullet." The costs of pensions are so easy to defer to our grandchildren. Moreover, public employes have been politically strong enough to forestall either needed modification of benefits or increase of contributions.

Martha Derthick's Policymaking for Social Security deals with a much larger and more important matter-- the national social security system. Her concern is not with deficiencies of the system, such as the alleged inequitable treatment of women. Her thesis is that the system has been shaped throughout the 44 years since it was established by no more than 40 people-- officials of the system, senior members of the two relevant congressional committees, a few business leaders and spokesmen for organized labor. This, she argues, is too few.

Despite its magnitude (nearly 35 million individuals now receive benefits each month) and its importance (it is the primary source of support for most persons over 65), successive presidents, secretaries of the Department of Health, Education and Welfare and an overwhelming majority in the Congress have played little or no part in guiding social security's growth.

Why? First, because social security met a real need. It was generally approved. Few wanted to criticize or even question. Second, the system is complex: only a handful of men or women have ever familiarized themselves with how it works. Third, it was in good hands: three eminently able, technically qualified and generally acclaimed men-- Arthur J. Altmeyer, Robert M. Ball and Wilbur J. Cohen-- were effectively in charge from 1935 to 1973. Derthick emphasizes that these little known individuals have been acclaimed by Republicans and Democrats alike, spokesmen for labor and for management, and by those scholars that have studied the functioning of the system.

The heyday for social security, however, came to an end in 1972. A principal virtue of the system had been its self-supporting nature: employers' and workers' contributions paid for the benefits. Each increase in the program had been sold on the assurance that revenues from the payroll tax would meet the costs. But, commencing in 1973, official reports projected a steadily increasing long-run deficit-- in 75 years, to be specific. Why?

Three factors account for the unforeseen deficit. Claims from disabled workers substantially exceeded predictions. The birth rate had declined; that meant fewer workers than forecast to pay taxes for a persistently growing number of beneficiaries. And 1974 introduced this country to unprecedented inflation (which increased benefit payments) along with high unemployment (which reduced payments into the fund).

The deficit was remedied fairly and squarely. Congress, late in 1977, increased taxes and adjusted benefits to cope with inflation more moderately. But the halo that social security had worn was tarnished. Partisan political opponents continue to point out that social security is not inviolate.

Derthick's book is informative, insightful and readable; her prescription for the future is theoretically unassailable, but questionable. She would have her readers believe that the shaping of the social security program in the future will and should be different. The role of the experts who have run the system should be limited. The workings of the system and especially its costs should be more open, subject to more partisan political debate.

In a democracy that is how public policy for such a governmental activity should be shaped. In practice, the complexities of this system (as of other government activities) are so great that the role of the administrative expert will likely continue to be large. Let us hope that social security will attract leaders as able and as dedicated to the well-being of those they serve as were those in charge from 1935-73.

The American people have a large stake in the shaping of future policy with respect to social security and all related plans. For this country cannot afford the growing costs of the accumulation of retirement systems-- social security plus public and private employer plans-- that now exist. It cannot afford to retire people between the ages of 40 and 60, as the length of life persistently increases; or to supplement wages and salaries for many for a fourth to a half of their working lives; or perpetuate the receipt by some of benefits from three or even four retirement plans.

Security of income for those unable to work in old age or for the truly disabled or for the survivors of workers who have died is essential in a humane industrial society. But this country cannot afford or justify heaping on future generations the mounting costs of numerous uncoordinated public, private employer, union and other retirement plans.