It is said we owe to the Middle Ages humanity's two most destructive inventions -- gunpowder and romantic love. But let this be said for the Middle Ages: people understood government. They especially understood that kings (read: presidents), not parliaments (read: Congress), are the principal impediments to reasonable public finance.

Kings were constantly siphoning off the nation's wealth to build palaces or liberate Jerusalem or, even more peculiarly, to explore what was to become Florida. Parliaments tried to pull the purse strings.

After 500 years of enlightenment, there is less understanding. Americans think Congress is the big deficit- maker. Never mind Lyndon Johnson's guns-and-butter choice, and never mind Ronald Reagan's guns-and-tax- cuts choice. Aer mind that while Reagan has been presiding over the production of more than half of this nation's federal debt, he has not found much to veto on budgeting grounds. This is because Congress has spent about what he has requested. And Congress has enacted as many balanced budgets as he has submitted.

Of course, presidents veto for other than budgetary reasons. Still, it is indicative that FDR averaged 43 vetoes a year, Eisenhower 23, and Reagan in his first term only 10 a year. Ten of this century's 15 presidents have used the veto more regularly than Reagan. But he is threatening to veto something, in part because of a provision that would reduce the deficit and cancer.

In 1951, the tax on a pack of cigarettes was put at eight cents. In 1982, it was raised to 16 cents, which because of inflation was much less in 1982 than eight cents was in 1951. The 1982 law stipulated a return to eight cents. However, one provision of the current deficit-reduction effort is to keep the tax at 16 cents. This provision was included in exchange for lavish tobacco subsidies.

Much of the deficit-reduction bill rests on cooked books yielding fudged numbers. The reduction number of $85.6 billion over three years is highly suspect. The $4.9 billion from the tobacco tax is real. But Reagan regards tax cuts the way Mark Twain regarded bourbon: "Too much is barely enough." Hence his insistence on cutting the tobacco tax. This will increase the annual cost of smoking-related diseases, which now stands at $35 billion.

This is tax folly compounded. The administration's tax reform plan is, by supply-side criteria, an irrational rearranget $25 billion from taxes on consumers, who demand goods and service; and it would increase taxes on businesses, which supply goods and services.

Folly is compounded, then cubed. The administration knows taxes alter incentives and believes they should be used to encourage behavior that is socially useful, such as saving and investing. Yet it wants to drive down a tax (on cigarettes) that discourages a behaviorally related disease.

Taxes . . . cancer. Let's talk about something else. Like AIDS.

The public has been told, repeatedly, that AIDS is the nation's foremost public-health problem. Many other problems have higher costs in suffering, death and economic loss. Many of these other problems are grounded in irrational behavior: drug (including alcohol) abuse, reckless driving, diet-related heart disease, lung cancer. But AIDS cases, we are told, are going to increase "exponentially." Maybe. However, if all the exponential growth rates recently predicted had occurred, the planet would have 6 billion inhabitants and almost no food or fossil fuels.

Intellectuals who postulate trends, and professions that respond to them, have emotional and vocational stakes in the exaggeration of the trends. Furthermore, George Orwell said intellectuals tend really to believe that a trend will go on forever -- that if Rommel gets to Alexandria he must get to Cairo. However, people learn things, such as how to decrease the risk of Rommel or AIDS or lung cancer. What Americans apparently cannot learn is the knack of reducing the ruinous byproduct of American democracy: deficits.

Because we have learned to connect clear causes and effects, we know that if the administration successfully insists on rolling back the cigarette tax, it will thereby increase the deficit by reducing revenues, and by increasing federal medical expenditures -- and by increasing what is already the fastest-growing component of the budget: interest charges.

What's that, you say? The Gramm/ Rud away deficits by "requiring" five annual cuts? It might -- unless it is repealed. There is precedent.

In 1978 Congress required that beginning with fiscal 1981 the budget be balanced. In 1980, Congress said: Well, er, change that business about the balanced budget from a requirement to an aspiration.

Now, what were you saying about the misconceptions, superstitions and peculiar rituals of the Middle Ages?