AS I SIT IN THE committee room where my colleagues and I are debating the various proposals for tax reform, I find myself remembering the words of Lyndon Johnson, who knew a thing or two about the legislative process.

"Reform," he once said, "is like whiskey. You can only take so much of it."

The very idea of tax reform is intoxicating. The present tax code, like real life, is messy, unfair and difficult to understand. In such circumstances, won't a shot or two of "reform" -- or a whole bottle of the stuff -- ease the pain?

Maybe. But the more I hear of this debate, the more I'm inclined to be a teetotaler on tax reform.

Two schools of thought are contending now.

One side sees the tax code as nothing more than a revenue pump -- a device for collecting as much revenue as possible from individuals and corporations.

The other, the side on which I find myself, sees the tax code not only as a revenue pump, but also as a device for promoting important national purposes. The tax code, my side argues, can and should play a pivotal role in advancing goals like home ownership, saving for retirement, capital formation by business and energy independence.

Right now the first side seems to be winning. The key question about any tax proposal has become a simple, mechanical one: "What is its revenue impact?" All but forgotten in the effort to produce a revenue-neutral tax bill is a deeper, more serious question: "How will it affect our ability as a nation to promote important national purposes?"

Let's ask that question about three current propsoals for tax reform:

First, the deductibility of state and local taxes: Under the present tax code, taxpayers are allowed to take a federal tax deduction for the state and local taxes they pay. President Reagan has proposed that we elminate this allowance -- and several "compromise" proposals, though they would preserve the allowance, would trim it.

Such proposals don't trouble people who belong to the revenue-pump school; eliminating the deduction for state and local taxes, or scaling it down, would certainly pump more dollars into the federal treasury.

But this "reform," if enacted, would also make it more difficult for state and local governments to raise money for important public services -- notably public education, which is financed overwhelmingly by local property taxes and state income taxes. If tax reform puts the squeeze on the ability of state and local government to support their schools, the much-publicized education reform movement, now getting under way, will be stopped in its tracks.

There's an irony here. President Reagan has talked a great deal over the past five years about returning power and responsibility to state and local governments. Meanwhile, he has pushed through a number of laws that have forced state and local governments to provide more services -- with drastically reduced federal help. Now he has set in motion a tax reform process which may end up squeezing state and local governments even harder. If this is reform, I don't like the taste of it.

Second, the rules governing state and local tax-exempt bond issues: Both the president's proposal and several compromise proposals would restrict the ability of state and local governments to raise funds by issuing tax-exempt bonds. The argument is that many such bonds actually benefit private businesses more than the public. When a city expands its airport with tax-exempt bonds, according to this argument, the new facilities principally benefit airline companies, which enjoy shiny new facilities paid for "by the public."

That argument has some merit, but not much. Airports are public facilities. Building or improving them helps not just airline companies, but the traveling public and entire local economies. Hobbling the efforts of cities and states to improve their facilities strikes me as not a particularly desirable reform. In any event, it's the opposite of returning power and responsibility to state and local governments.

Third and finally, tax advantages for businesses: Under current reform proposals, several familiar business tax advantages will be cut back or dropped altogether -- among them the investment tax credit, the percentage oil depletion allowance and the recovery by oil companies of so-called intangible drilling costs.

One man's "incentive," I know, is another's "loophole." And as a member of Congress from an energy-producing state, I can be accused of bias. The fact remains, however, that our government depends on private business to advance some major public purposes: job creation, economic growth and energy security among them. No recent president, incidentally, has been more vocal than President Reagan in trumpeting the role of private business in solving public problems.

We ought to be careful, in my judgment, about tampering with the incentives which encourage businesses to make the investments that lead to job creation, economic growth and energy security. And we should be especially careful when it comes to encouraging domestic energy production.

Why? Because our nation's future economic growth depends heavily on adequate supplies of energy -- and our military security could someday depend on adequate supplies of domestic oil and gas. Little more than a decade ago, the Arab oil embargo dramatized our dependence on foreign energy suppliers and helped set off a disastrous round of inflation. Those troubles are only memories now. But they could return if we go too far with reforms that discourage energy producers from taking the risks and making the investments that are needed to guarantee adequate supplies of domestic oil and gas.

Why am I so disturbed? Because of another irony: Taken in their entirety, the tax reform proposals of the Reagan administration -- presumably a conservative, business-oriented administration -- would make the recovery of capital investment less advantageous in our country than in virtually any other industrialized nation.

The president and the revenue- pump school of tax reformers need to study the words of Edmund Burke. The truest conservatism, Burke once said, is that which "lops off the dead branches to preserve the living tree." That's how we should be approaching tax reform. Unfortunately, however, the president has proposed -- and Congress is flirting with -- radical changes which threaten to uproot the tree.

How did this happen? As with so many mishaps and disasters in Washington, we are about to come up with the wrong answer because we are asking the wrong question. We have become fixated, in the current debate about tax reform, upon a question asked by the president: Can we lower tax rates without sacrificing federal revenue?

By struggling to answer "yes" to that question, the Congress has set in motion a process which threatens to jettison not only unfair "loopholes" in the existing tax code, but also many valuable incentives, carefully put in place over the years, for advancing key national goals -- incentives which aren't broke and don't need fixing.

In 1980, the president posed another dubious question to the Congress: Can we lower federal taxes, and raise federal spending and still not suffer runaway deficits? Congress answered "yes" and the dismal results will be with us for years to come.

That's why, as I sit in the Ways and Means Committee room, I'm remembering Lyndon Johnson's maxim about reform and whiskey. He was thinking about the hangover that too much of either, carelessly imbibed, could produce. So am I.