IT IS A PITY, when you think of it, that so many of our unfortunate citizens are prevented, by reason of age, from joining the Army or seeking civilian employment with any branch of the armed services.

If they could somehow put themselves under the protection of the military, they would enter a new world where Ronald Reagan's philosophy of "austerity for the deprived" could not reach them.

Presently, thousands are undergoing a review of their eligibility for Social Security Disability payments. Earlier this year, Sen. Carl Levin (D-Mich.) brought to the nation's attention a man named Richard Kage, who had to to prove to Social Security officials that he was really sick. The potentially life- shortening review process goes on. The smaller the budget, the more intense the scrutiny. That seems to be the rule followed by our young budget director, David Stockman, who like his boss, does not wish to see any undeserved dollars trickling down.

Every nickel and dime counts in the federal budget, except at the Department of Defense, where they ended up with $2 billion left over in their budget. Did they turn it back to the Treasury Department to help shrink the deficit? Certainly not. They know their duty. The found ingenious ways to spend it.

They ordered a new self-shining boot, a plastic helmet that costs $100 per copy, and they have offered to soldiers a designer fatigue outfit which shrinks only 10 per cent when washed. Moreover, they bought 17 ladders for $594.34 each, which, if they had not been under the pressure of their tradition of cost overruns, they could have had for $160 apiece.

Other people who receive government checks are being encouraged to examine their consciences and to think of what they can do for their country. The jobless have an obligation to think of unemployment as "less attractive." Flood victims are expected to do more with less federal insurance. The sick may pay health-insurance taxes. Many sacrifices are still to be made, although not at the Pentagon.

The Department of Defense is the one government agency that enjoys the complete approval of the president. He knows that it is not like other government departments -- it is free of fraud and waste. The Department of Defense is a noble institution, not like those crafty individuals who feed at the public trough -- and buy vodka with food stamps, feign illness in their old age and shamelessly insist they can't find jobs.

The commander in chief will brook no talk of Pentagon failures. Some of them are fairly well documented, like the FA-18 plane, whose initials stand for "Fighter-Attack," which can't do either. It's too slow to fight, and in its last test it fell short of its attack range by 180 miles. The Pentagon wants to build over a thousand of these birds for $40 billion dollars. The administration's answer is "Why not?" It is, after all, only money.

Read the House Appropriations Committee report on the 1983 Department of Defense budget request and you will how the notion of the larger life persists at the Pentagon.

For instance, our defenders propose to rid themselves of the onerous burden of having to buy passenger automobiles that get more than an average of 22 miles per gallon. It is status-destroying to travel in those fuel-efficient compacts, which can make such a dense pack of generals riding to Capitol Hill to explain the department's splendid energy-conservation program. The limousine is ever so much more reflective of their lifestyle.

"We in the Department of Defense have a responsibility to seek economies and efficiencies in all we do," Secretary of Defense Weinberger has been quoted as saying.

But the public affairs division know he doesn't mean them. They are the folks who brought you releases boasting about the department's energy-conservation program. They want an increase in their allowance, from $3l million to $32.9 million. How else will a little old lady, denied federal fuel assistance, and shivering in a tenement, know how wonderful they are?

Recently, the Pentagon announced an expansion in its polygraph activities. It uses lie- detectors to find out who leaks embarrassing information about their extravagances to the press. Maybe somebody should use it on the top brass. Ask them if they really need all of the $231-billion budget the House voted them this week. A lot of people living on Social Security and seeing their "window of vulnerability" opening wider would like to know.