One of the biggest and least visible minority groups in the Washington area is its 100,000 federal and military retirees. They ran the show when most of us were kids. Not all of them were worldbeaters, but the majority did nice work under some difficult circumstances.

Now, many of the retirees feel isolated and betrayed by a new generation of politicians and voters who either ignore their contributions or seek to balance the budget by trimming benefits for old-timers.

Today's first letter to the Monday Morning Quarterback is from an 80-year-old U.S. retiree. He asks younger people to reflect on what they owe the old-timers:

"I am ashamed to see what so many people think about our government employes and retirees. There is no free country in the world where government workers are so discriminated against. I think it is due to frequent political changes. Are the people who want to make changes saying that former officials and administrators who designed the federal pension system were stupid?

" . . . I joined the government in 1936. We old retirees helped you people when you were little more than babies to ensure that you have a free country now. Aren't we entitled to get a little credit from you? I lost my house, job and savings during the Great Depression and worked through World War II.

"You young people voted for the present bosses and don't complain now.

"What we retirees have to face because of the Gramm-Rudman-Hollings act is the prospect of a pension freeze through 1991. Don't let it happen." R.W., Annandale

"Your March 20 column noted that some congressional Democrats are 'skeptical' about the motives behind Sen. William V. Roth's (R-Del.) proposal to open an early retirement window this year for federal workers. It is pretty obvious those 'skeptics' are more interested in being Democratic precinct captains than in protecting the interests of federal employees. The Roth bill is one every fed ought to hope becomes law even though (heaven help us!) it is sponsored by a Republican. With friends like the Democratic staffer you quoted, who needs enemies?" J.K. in Kansas City, Mo.

"Some retirees say they're happy to give up cost-of-living raises to reduce the deficit. In fact, retirement fund expenditures don't increase the deficit . . . . The fund has assets of over $124 billion and is growing.

"Instead of being part of the deficit, our fund is used to help finance the deficit because all federal trust funds are invested in government securities . . . . the funds should be placed 'off budget' and invested in the private sector to maximize earnings. Also, the government should be barred from doing what it did last fall, borrowing from the retirement fund to help get the government through the fiscal year because Congress failed to approve budgets." K.W.J., Waldorf

"You correctly point out that the pension tax changes proposed in the tax reform bills before Congress could cause thousands of civil servants -- including many of the most experienced and valuable -- to retire sooner than expected.

"I have discovered that sane people intend the foreseeable consequences of their deliberate acts. Accordingly, I assume that the administration and Congress intend to encourage the retirement of those civil servants. Afterward, however, look for some politicians to claim that they did not realize what they were doing as they have already done when the Gramm-Rudman-Hollings act cuts out important and sensitive programs and services." G.E.T., Alexandria