Top Reagan administration officials who insist that federal employe morale has improved in the past four years are invited to come to this office and spend some time opening -- and reading -- letters from civil servants who apparently don't know how happy they are.

Federal workers -- not just those in the Washington area, either -- appear to be very unhappy. Some think the administration is misguidedly trying to balance the budget on the backs of government workers. Others think it is trying to destroy the career civil service -- and doing a pretty good job of it.

Recent letters to the Monday Morning Quarterback are not much fun to read. But they are from real people, some very ordinary and some very important, whose letters normally would not get through to the boss. Here are some of them:

* "Changing the retirement system [it was changed years ago to make room for 'new young blood' that has since gotten older] should be thought out more carefully, and changed only if the pay system is revamped to be in tune with expected additional years of work.

"My career is about over in the federal service. I have made no big advances in my career, or any big marks to be remembered. I just did my job. If I had it all to do over again, I would have second thoughts." J.F.L, Arlington.

* "Why doesn't the president make some of the sacrifices he wants everyone in government to make? He could give back his salary, since he has no living expenses . . . cut back on some vacation trips to California . . . cut back his White House staff . . . . Then maybe we would be willing to share." L.B., Washington.

* "We the willing, led by the unknowing, are doing the impossible for the ungrateful. We have done so much for so long with so little we are not qualified to do anything with nothing!" A federal worker from P.G. County.

* "I know I am a rebel within government, however, I must live with myself. I personally feel that the federal employe is overpaid, underworked, lazy and much more. They should not have the right to retire then get another job when people on Social Security can't do it, and have worked a good deal harder and longer than any federal worker I know of, including myself. Lest you think me a crank, I am over 50 years of age, have worked in the federal government for only 9 years, having spent approximately 16 years working in private industry before my family came along." P.S. Fairfax.

* "Please Mr. President, cut my leave. I really don't need it. I don't have any work to do at home and the maid takes care of the housework and the children so don't pay me for doing nothing at home when I can go to work and feel more positive about my lack of productivity.

"Please, cut my retirement. Make all of us work longer. We can help the budget and fill the halls of government with people with walkers and put benches in so the elderly employes can keep working and not draw retirement.

"Please cut my health benefits. I only pay one-third more than anyone in industry I know. I could not bear the thought of denying the Pentagon one of those $5,000 coffeepots, or $100 bolts so vital to our national defense.

"When all the cuts are made, Mr. President, I can stand tall knowing that I have helped you keep America strong and free. I will have become part of that indomitable spirit that has pulled this country through the era of self-criticism and doubt caused by weakness in the past. You've inspired us all. Thank you!" The Federal Employe.