ohn F. Kerry hadn't even been elected lieutenant governor of Massachusetts yet the last time the government down here went off its rocker.

So you should forgive his rational exuberance last week in assaulting the idea that tax cuts that leave a hole in the country's balance sheet are anything but absurd and obscene.

''Something must be in the air in Washington,'' he said last week, in between performances of his high-profile role in the opposition. ''We're talking about a deliberate recipe for permanent fiscal crisis.''

Kerry may have missed the original fight 18 years ago. But he brought to last week's more political Senate battle the experience of having bested Bill Weld three years ago, when the then-Guv may have been the only Republican running (Bob Dole included) who vigorously backed the GOP presidential nominee's silly proposal to cut income tax rates across the board by 15 percent.

Kerry whipped Weld by arguing then, as he argues now, that deep tax-cutting is a stalking horse for deep government-cutting that folks on the right either can't or won't propose in detail and thus want to force throught the back door.

Of course, that was a major chunk of the crusade to slash taxes back in 1981, when Kerry had yet to fight his way onto Mike Dukakis's comeback gubernatorial ticket, just two years before he succeeded Paul Tsongas as senator.

Back then, Ronald Reagan talked tax cuts as analogous to the cutting of a child's allowance. Today, his less restrained descendants scream ''starve the beast'' on the floor of Congress.

But back then, Reagan could also talk about reviving an economy headed toward the worst recession since the Depression and wrestling with ruinous inflation and high interest rates.

Today, in near-perfect economic conditions, a large tax cut makes no economic sense, and so it exists only to suit an ideological goal. Tax Cut '81 and Tax Cut '99 share one important feature, however. Both are premised on the demonstrable fiction that they are fiscally responsible and won't run up deficits that can smother the economy's ability to generate higher living standards.

Reagan never proposed and Congress never enacted a budget that would have balanced - hence the preposterous explosion of debt by some $4 trillion. And the current Republican Congress - pressing mindlessly ahead with its veto bait, $792 billion red-ink recipe - blithely assumes the appearance over the next decade of a nearly $1 trillion surplus outside the Social Security trust funds; and this nonexistent sum must be ''returned to the people'' to prevent the alleged catastrophe of its being ''spent.''

Part of Kerry's function last week as one of Democratic leader Tom Daschle's high command, was to demolish the ''surplus'' fiction; the other was to be one of several Democrats offering symbolic amendments to illustrate the warping of national priorities that radical tax-slashing can cause. In performing each task effectively, Kerry was acting more in the tradition of what used to be known as a moderate Republican than in the role of traditional Democrat.

On economics, Kerry has always had a touch of ''neo'' about him. He is conservative fiscally, concerned about the cost of investment capital, not averse to lower capital gains taxation, and a booster of the new technology industries.

With the tax debate's best pie chart, Kerry showed that more than half the alleged surplus outside Social Security (nearly $600 billion) consists of an assumption that for 10 years the nonentitlement program budget - military and domestic - will never be adjusted for inflation.

The truth is, he noted, that Congress is already well outside that box and will go even further. And the additional truth is that Congress should permit some increases and some decreases in basic governmental functions.

In addition, Kerry's chart showed that the ''surplus'' assumption has no room for real emergencies and no provision for unavoidably higher Social Security administration costs. And since realistic budgeting means a more gradual lowering of debt interest costs, the bottom line is at the very most a 10-year operating surplus of a bit more than $100 billion. And that figure stands without a dime invested, as will inevitably occur, in Medicare.

And it was on one aspect of Medicare that Kerry's clever amendment focused. It would have reduced the tax cut's size by just 3 percent.

But those $20 billion or so would have cushioned the program from the well-documented damage that deep cutbacks affecting nursing homes, home health care, and teaching hospitals have caused. Those cutbacks are running at double the rate planned when Medicare providers were targeted as part of the balanced budget agreement two years ago.

Kerry came close on the floor, losing 51-49. Three New England Republicans backed him (retiring Senator John Chafee of Rhode Island and Olympia Snowe and Susan Collins of Maine). He was stiffed by Jim Jeffords of Vermont and by New Hampshire's men of the right, Judd Gregg and Bob Smith. But those three plus Jeffords are also proponents of a presposterous $500 billion, cupboard-emptying tax cut.

It was thus 18 years ago. Only one current GOP senator who was here (Jeffords, then in the House) opposed the 1981 disaster. Only one, Bill Cohen of Maine (now defense secretary), opposed the Newt Gingrich budget in 1995.

On economics, today's moderate Republicans in New England are in fact represented by John Kerry from Massachusetts and Joe Lieberman from Connecticut.

Thomas Oliphant is a Globe columnist.