Whyare they making it so hard? In a budget well over $1 trillion and an economy approaching $6 trillion, you'd think that a president and Congress could find $40 billion of deficit-closers without all the past week's dramatics and hysteria.

The politicians know that most of the country regards this performance as ludicrous. But they also know with painful clarity that the voters who denounce the budget impasse as absurd are the same voters who can swing against them with vengeful fury over an increase of a few cents in the gasoline tax, or a modest trim in Medicare.

One of the hardest and most dangerous exercises in democratic politics is to change the balance between what people are used to paying their government and what they are used to getting for it -- especially when that requires cuts in long-established benefits. The origins of this mess lie a long way back, in the early 1970s.

The last time that the budget was balanced was in 1969, the final year of Lyndon Johnson's presidency. When Richard Nixon came to office he immediately cut taxes and, on a gigantic scale, increased federal benefits to individual recipients.

It seemed reasonable at the time. Under the circumstances, most people thought that the country could afford it.

By the late 1960s the great postwar boom had been running for nearly a quarter of a century, carrying all the industrial democracies to levels of prosperity beyond any limits that even the optimists had believed possible. It was the longest and most powerful surge of economic growth in history. There had been minor recessions from time to time, but the underlying trend upward had remained astoundingly strong.

Success breeds hubris. Politicians began to believe the economists who assured them (incorrectly, as it turned out) that with good management the boom could be kept going indefinitely. They began taking fast growth for granted. That left only one question, the pleasant one of deciding how to spend the revenue that this phenomenal growth was bringing to public treasuries. Here in the United States -- and, incidentally, in most of the other rich countries -- there was an explosion of spending on social benefits in the early 1970s.

Non-defense spending rose faster under Nixon than under Johnson's Great Society, or for that matter under Roosevelt's New Deal. Federal benefits paid directly to individuals rose from 6.1 percent of GNP in 1969 to 10.1 percent in 1975, where they have remained ever since. That was the period in which the pattern was set for the present generation. This year's deficit estimate is, incidentally, just about 4 percent of GNP -- almost precisely the cost of the Nixon benefit increases.

There was little controversy about it at the time, and few people were aware that the country had passed an important turning point. Unlike the Great Society, this spending was driven chiefly by benefits to middle class people who voted -- above all, rapid expansion of Social Security and Medicare. A historian would say that it reflected the temper of the time and the long postwar boom rather than either party's agenda. But it wasn't a plot by the spendthrift Democrats. This explosion of benefits was actively and vigorously promoted by a Republican president who took full credit for it in his highly successful reelection campaign.

But, as often happens in human affairs, the good fortune of fast growth ran out just as everyone had begun to count on its lasting forever. With the oil crisis of 1973 and the severe recession that followed, deep changes overtook the economy, and it shifted to a path of lower growth that has persisted to the present. Lower growth has meant consistently insufficient tax revenues to pay for the expanded entitlements. The year 1975 is the point at which the era of the intractable deficits began.

By 1990 nearly everybody has forgotten that when the budget was last balanced, taxes were significantly higher than now -- and that entitlements were much, much lower. Things have now been as they are for two decades, and both the tax rates and the entitlements are fixed in American political custom.

In the present atmosphere of evasion and maneuver, no one in office is willing to explain to a baffled and increasingly irritated public why, after all these years, a deep and unwelcome change in budget policy is required -- what it is that makes this year different from the past two years when the same President Bush said that no change was needed, or the eight years before that when Reagan was saying time would take care of the deficits. It's understandable that, in the absence of any coherent explanation, voters threaten to take vengeance on politicians who try to impose higher taxes and lower benefits.

The truth is that nothing has greatly changed in the past year. Despite the assurances of all those people in high office over the years, the present level of taxation has never been adequate to finance the benefits legislated of the Nixon years.

Ever since the Reagan tax cuts of 1981, the United States has depended chiefly on a flow of money from abroad for that financing. The present sense of crisis has been generated by hints and signals that, because of events far from this country, that crucial flow is now beginning to dry up. Bush is trying to tell the country that it has to prepare to live on its own earnings -- but he can't quite bring himself to explain why.

The writer is a member of the editorial page staff.