Government-oriented Washington is sympathetic when U.S. agencies warn of a brain drain if Congress changes pension tax laws covering civil servants.

But beyond the Beltway many people cheer -- rather than fear -- the prospect that thousands of government employes might quit early. Would the taxpayers win, or lose, if many high-salaried (and high-skilled) feds pulled the plug?

Today's leadoff letter to the Monday Morning Quarterback is from a 30-year government engineer, who loves his work but says he will quit if tax rules are changed:

*"I'm an engineer with the Energy Department . . . . I recently received an award for directing nuclear fuel reprocessing activities.

" . . . I could retire today. But I enjoy my work and consider it important. The department hasn't hired young engineers for many years to learn skills [practiced by] its more important staff and I expect the same is true of other agencies with important technical programs.

"I had planned to retire at 65 . . . . Purchase of U.S. Savings Bonds has been particularly attractive to some of us . . . . All my financial planning and investments have been based on a promise that my retirement annuity will not be taxed until I have recovered contributions on which I already paid taxes.

" . . . My present salary is $66,000 a year. My annuity would be about $40,000. So the government is paying its lead professional in an important area about $26,000 per year net. And there are many of us."

"My career spans a period when federal service was considered important. But during the past 10 years there seems to have been an effort to devalue its importance." DOE Engineer

*"Regarding the civil servant who wrote a letter to a job-hunting student discouraging him from seeking employment with the federal government:

"This is an outrage. Where is his loyalty? If one wants to criticize the federal government (outside of your own chain of supervision) one should first resign. There is an old saying that 'if you eat the king's bread, and drink the king's wine, you serve the king.' Apparently these people never heard of loyalty to one's employer." R.E.W., Arlington

*"Allow me to reply to persons who said that cost-of-living adjustments (COLAs) have no effect on the deficit. COLAs aren't paid out of the retirement fund . . . but out of general funds. Each year the Office of Personnel Management's appropriation fund is charged the amount necessary to pay COLAs for the coming year . . . . These COLAs become part of the base from which future raises are calculated. If money isn't available from the general fund (as now) it must be borrowed, thereby adding to the deficit.

" . . . I doubt that anyone is 'happy' to forgo a cost of living raise . . . . However I would be most willing to do so if this problem of the escalating federal retirement system cost could be solved." Olive Hunt, National Committee on Public Employee Pension Systems

*"One aspect of the House plan to end the post-retirement tax-free period for federal workers that has been overlooked concerns individual retirement accounts (IRAs). I made IRA contributions based on the government promise that I could withdraw it during my first year of retirement at a minimum tax rate since my pension won't be taxed for the first 18 months or so. If Congress changes the rules, the federal contribution to my pension is immediately taxable along with the amount I withdraw from my IRA. 'Tain't fair!" N.A., APO, N.Y.