(FORTUNE Magazine) – Dear Mr. Statistics: I am 68 and used to dozing off any time the national debt comes under discussion. But now the fellows at the tavern tell me interest on the debt is rising more rapidly than federal revenues, so eventually the day will come when all the revenues must be applied to interest payments, leaving nothing for my civil service pension. Does this mean I will have to go back to work? -- Wide Awake Now

Dear Wide: The news is good: You are heavily favored to die before interest on the national debt exceeds total federal revenues. Late estimates for the decade ending in fiscal 1993 show the national debt growing at an annual rate of 12.7%, federal revenues at 6.8%. Projecting these trend lines into the future, and assuming the government pays an average of 7% when it borrows, interest payments will not consume all federal revenues until 2018 (when both figures will be around $6 trillion). The odds against a 68-year-old male living until then are 20 to 1, and higher for barflies.

Dear Mr. Statistics: Astronomer David Morrison of the Near-Earth Asteroid Detection Workshop is one of many scientists stating that there is a roughly 0.000001 (one-in-a-million) chance each year of my favorite planet's being clobbered by an asteroid large enough (several miles in diameter) to extinguish all human life, just as past generations of asteroids are said to have done in the dinosaurs. These scientists also state that for a $50 million investment, we could build a computerized telescope system capable not only of identifying all the troublemakers whizzing around out there but of providing ten or more years of warning for any aimed in our direction. Asteroids that threatened to do a brontosaurus job on the people could then be nonchalantly knocked off course via nuclear explosions in space. Yet I am skeptical. While undesirous of sending Mr. Evolution back to the starting gate, I smell a high-tech pork barrel. Kindly perform a right-wing cost-benefit analysis to see if my dubiety is warranted. -- Revolting Against Pork

Dear Revolting: We begin by identifying the core question: Would the cost of not building the telescopes exceed the $50 million cost of building? The cost of not building, i.e., of remaining unprotected against asteroids, may be conceived as the value of the lives lost in the catastrophe multiplied by the annual 0.000001 probability of its actually occurring. In calculating this number, we begin by limiting our concerns to the coming 100 years. Next we assume that an average American life is worth $3 million (a figure mentioned respectfully in a March 3, 1986, FORTUNE article called ''How Much Money Is Your Life Worth?'') and that the number of Americans, now some 250 million, will rise at a rate of 0.6% per annum (a mainstream projection). We also assume that the U.S.A. will end up bearing the entire cost of planetary defense during the century and therefore hard-nosedly assign a zero value to the lives of freeloaders abroad. With the fate of humanity hanging in the balance, we turn tremulously to the PC monitor, on which is displayed a spreadsheet depicting the cost of doing nothing. In column one, it shows the U.S. population rising over the century from 250 million to 452 million. In column two, we show the nominal value of each life rising (because of assumed 4% inflation) from $3 million to $146 million. In column three, we show the results gained from multiplying the figures in column one by those in column two, then adjusting this product to reflect those one-in-a-million odds. Column three now has 100 entries assigning an ''expected value'' to the cost of human extinction in each year from 1992 to 2091. In case you are wondering, the figure for this year is $750 million. That is the cost of being unprotected against asteroids right here and now. Costs for each of the next 99 years must of course be discounted back to the present. When told to assume a 7% discount rate, Lotus 1-2-3 instantly reports that the ''net present value'' of those 99 costs through 2091 is $28 billion. We are now at the cost-benefit bottom line: The cost of buying the telescopes is $50 million. The cost of not buying -- synonymous with the benefits derived by buying -- has a present value of $28 billion. By a process known as ''visual inspection,'' we ascertain that the latter number is quite a bit larger than $50 million, meaning that the telescopes are a steal. Folks worrying about pork barrels may of course riposte that this calculation is built on ''soft'' data. Okay, there are no hard data, especially on the value of a human life. But look at it this way: If you accept our other inputs as reasonable guesses about future inflation and population trends, then a decision not to buy telescope protection is one that implicitly values an American life at less than $560, about the price of a decent suit in the men's department at Saks Fifth Avenue. Even for us right- wingers, that figure looks low.