THERE IS A WINDOW of vulnerability in our family transportation system. A subcompact station wagon seating four with 60,000 miles on it no longer provides essential equivalence against enemy cars on the Beltway for a five-member household that includes one baby (and her equipment) and one teen-ager who has expanded to over six feet. We are cramped, grouchy and unsafe. Our car is inferior to newer, larger cars and in a confrontation, we could lose. We have brought in consultants and done feasibility studies and come to the conclusion that the family's margin of safety depends on the installation of our lives of the biggest, sturdiest, safest car possible -- the latest word in large station wagons, in other words -- fully equipped.

There is, of course, only one problem with that. The cost of station wagons has risen along with everything else, and what we got for $4,000 five years ago cannot be replaced for less than twice that sum. That is going to cause an imbalance in our budget, roughly equivalent to the trade deficit we now have with Japan. Fortunately, the Reagan administration is showing the way on this and the solution for us is clear: We will simply cut domestic spending.

I have proposed an immediate, across-the-board cut in all health and welfare costs. No visits to the doctor unless the kids are truly needy. Routine checkups will be indefinitely postponed unless the child also has a high temperature or broken limbs. Dental needs will be postponed until everyone has his permanent health.

No more school lunches. They'll just have to eat hearty at breakfast and hope their stomachs don't make too much noise in class.

No more recreation. I do not believe it is the function of a family to provide recreation. People should learn to amuse themselves.

No more pets. There is no reason to think anyone would pay admission to see our cat and since he cannot make himself self-sustaining, I am proposing that we donate him to a nearby zoo. He is getting rather old anyway and people have much more modern cats in Baltimore.

No new clothes, except for the truly needy. A hole in one knee of a pair of pants does not qualify a person as being truly needy. Pants that are embarrassingly short on growing children will simply be reclassified as Bermuda shorts.

No more alcoholic beverages and no more expensive soft drinks. Both lead to shiftlessness. Also, no new televisions, stereos or radios which encourage laziness and loud noise and distract family members from what they ought to be doing, which is to concentrate their full time and attention on finding ways to make money so we can pay for our station wagon.

I, personally, intend to deregulate the household so that I no longer have to stay up evenings making sure that children are home on time and can either go to sleep or get a part-time job to help pay for the car. I expect my husband to lower some of his regulatory standards so that we will spend less time watching after the welfare of family members and can spend more time making money to afford our car.

No more flowers, garden plants or other expensive luxuries that might soften the eye, but cost money. I am commissioning a feasibility study to see if the front and back yards can be converted into corn fields that could ultimately produce gasohol for the station wagon, and if any neighborhood activists start complaining about the effects of my corn fields on the environment, I'll tell them to hire a Neighborhood Legal Services lawyer and I'll see them in court.

No more tuition aid for our children. They can work nights, weekends and summers to earn money. If I did it, then by golly, so can they.

No more child care for the 5-year-old while I work. President Reagan thinks a lot of those welfare kids can take care of themselves without government help, and if they can take care of themselves, then so can mine.

We will sell all bikes, which are a continual drain on the family economy since they get flat tires and bent fenders and their lights constantly need new batteries.

I have estimated that 25 percent of our family food budget is frittered away in waste, fraud and abuse. To curb family abuse of food, I have ordered an across-the-board cut in food consumption. Borrowing a page from the book of Paula Hawkins, the new Republican lady senator from Florida, anyone who is cut cheating on food will be thrown out of the family and jailed.

These are, I have to admit, drastic measures, but it is going to take drastic measures to get our budget balanced and to make our family safe on the Beltway. I had hoped that the tax rate cut would be enough to cushion the impact of our defense program, but I've now figured out that the savings we will get in the Reagan tax proposals will be just about enough to pay for tires.

But things aren't as bad as they seem. We will be safe in our new car and warm in our new home. I have also ordered that the heat be turned up from 62 to 72 degrees in the house so the oil companies can make money, which will give them an incentive to drill for oil. After all, if the corn crop fails in the front yard, we have to have something to put in the car.