WHAT MAY BE the most comprehensive survey of public attitudes toward taxes ever conducted shows that Americans are solidly behind President Carter on the need for tax reform and largely behind him on most of the individual tax changes he has submitted to Congress.

The results of the survey, conducted by the Roper organization, were issued July 26, just as Congress was savaging the remnants of the Carter tax program. Past administrations would have made sure such a survey was widely reported, and would have used its findings to generate public pressure on Congress on behalf of the president's program. But the Carter White House apparently has made no use of the Roper survey, and the media have largely ignored it. A Washington Post account of the poll pointed out some of the pluses for Carter, but its theme was expressed in the opening words: "A new nationwide tax survey yesterday brought bad news for President carter."

Bad news? Not really. On a list of nine broad tax themes or specific proposals, the Carter position finds support from the public on seven. On the eighth, having to do with capital gains taxes, the poll shows division. On the ninth, dealing with a proposed tax credit for dependents in lieu of a tax ememption, Carter is a narrow loser.

One of the most highly publicized parts of Carter's original tax proposal, the so-called three-martini lunch, would have made only half the expenses for a business meal taxdeductible. The public supports that by a 6 to 1 majority, according to the Roper poll.

Carter's program, virtually none of which remains alive, would have cut taxes by $25 billion, with 94 percent of the relief earmarked for individuals and families with incomes of $30,000 or less.(Because of a rise in incomes since the proposal was made, had the plan gone into effect now, 88 per cent of the relief would have gone to such people.) On July 27, the House Ways and Means Committee approved a $16 billion tax cut, its key feature being a reduction in capital gains taxes. Under that plan, from 53 to 55 percent of the relief would go to families or individuals with incomes of $30,000 or less.

Barber B. Conable Jr. (R-N.Y.), the ranking Republican on the Ways and Means Committee, said that the committee's tax proposal "reflects the American people's view of tax reform because it is a tax reduction," and that "it helps the middle-class taxpayer in a manner much more substantial than the traditional tax reform bill."

The second part of that statement may be open to interpretation, since it is not clear to many where "middle class" begins and ends. But the first part is bunk.

The Roper firm interviewed 2,007 adult Americans nationwide in May, and found tax reform considered the third most pressing problem in the country, ranked only behind controlling inflation and curbing crime. Lowering taxes was listed toward the bottom, at tenth on the list.

As Burns Roper pointed out in an interview, that should not be regarded as meaning that Americans don't want taxes cut. They do. In fact, they felt it was much more important to keep Carter's full $25 billion tax cut than to hold the line on taxes and the national debt. "I think there is a desire for reduction," Roper said. "I don't think it is the number one thing."

Further, it is quite clear, despite Conable's assertion, that Americans do not equate tax reduction with tax reform. They see tax reform in the same terms that Carter uses to describe it.

One question asked in the survey was this: "When you hear the words 'tax reform,' which of these things does it mean to you?" Six possible "meanings" were offered as choices: making taxes fairer to all, tightening up tax loopholes, making taxes "fairer to people like you," making tax forms simpler, reducing "your personal taxes" and raising "your personal taxes."

Seventy-six per cent of those interviewed said tax reform meant either making taxes fairer to all or tightening up loopholes. Only 5 percent said tax reform meant that their taxes would probably go down. Widespread Misconceptions

OVERALL, the poll shows that, in Roper's words, "In the view of the American public, the major problem with the federal income tax system in this country is its unfairness . . . A growing majority sees middle income families as overtaxed, while upper income people and large businesses are seen as undertaxed . . . The public places high priority on tax reform to make the system fairer." That could be Jimmy Carter talking.

What led the Washington Post reporter to state that the Roper poll was bad news for the president was a discussion of capital gains taxes included in the report. As interpreted by Roper, the public sides more with Congress than with the president on capital gains.

The findings, however, are not clear-cut. As the law now stands, the capital gains tax works so that people pay taxes on a maximum of 49.1 percent of the profit they make from the sale of stock or property. Carter proposed originally to make all such profit taxable. The Ways and Means Committee measure would make the maximum captial gains tax apply to only 35 percent of the profits from the sale of stock and property, and would exempt entirely the first $100,000 in profit from the sale of a home.

The Roper survey questionaire listed 11 types of tax deductions, exemptions and nontaxable items permitted under present tax law. Those interviewed were asked whether they felt each tax break, including the capital gains provision, was reasonable or whether it represented a loophole.

Forty-three percent said they considered the existing capital gains tax provisions reasonable; 40 percent said it was a loophole. Only one other item, the tax-free state of interest from municipal bonds, drew more opposition from the public, with 43 percent calling it a loophole. In other words, Jimmy Carter could claim from the data that, of all the loopholes that anger people about the tax system, capital gains is at the top of the list.

Roper concludes from the 43-40 split on capital gains that it is considered by the public as a reasonable deduction. To others, the margin is so slight that it might appear to represent a split right down the middle.

In addition, it may be reasonable to assume that a sizable majority would view the current congressional proposal as a loophole if they perceive that it would result in what Jimmy Carter says it would: "A windfall for millionaires."

In an interview, Roper himself would not draw that conclusion. He said that the public seems to be saying about capital gains, "Leave it as it is." He feels that the Ways and Means proposal is closer to public sentiment than Carter's original proposal, but that his poll "is not a clear win for Carter on Capital gains, and not a clear win for Congress, either."

Roper, who conducted the study for the H&R Block tax firm, offers abundant evidence that there is "a widespread misunderstanding of, and lack of information about, how the tax system works." Taxpayers overestimate the percentage of income they themselves pay and underestimate the percentage that high-income people pay; one-quarter of the people think "a tax-deductible contribution costs the giver nothing because it can be taken off in income taxes."

It might not be wise policy to structure a tax program around attitudes that are formed partly by widespread misconceptions. Nevertheless, if public opinion is to be cited in the tax debate, it seems only fitting to point out what the public really does think.

And if polls that show Carter doing poorly are highly publicized, as they are, those that show him in a favorable light ought to be publicized as well.