The first response to Treasury Secretary Donald T. Regan's proposed revision of the income tax code largely has been one of derision. A variety of pressure groups -- the U.S. Chamber of Commerce, real estate and oil groups, other business interests, big labor, state governments, Wall Street -- are opposed. President Reagan is said to be cool to it.

With that type of reception, it might appear that the proposal has some features that appeal to the private citizen. It does.

The fact is, despite details that may antagonize many middle-class people as well as the wealthy, the thrust of Regan's modified flat-tax proposal is closely in line with what the broad masses of citizens want, as shown in numerous public opinion polls, including a new one done for the Internal Revenue Service.

The proposal calls for individuals to be taxed at 15, 25 or 35 percent of their income. It would allow homeowners to continue to deduct interest on mortgage payments but would close loopholes that allow the wealthy to pay few taxes. It would move toward restoring to some degree corporate taxes that largely have been eliminated under the Reagan administration.

It also aims at taking the complications out of filing tax returns, so that citizens would be able to figure out what they owe without becoming bookkeepers or having to hire accountants. In one regard the plan is the essence of simplicity: Many taxpayers would not have to file any returns. By 1990, according to Internal Revenue Commissioner Roscoe L. Egger, the elimination of deductions and credits could make it possible for IRS to do the tax work for two of every three taxpayers.

Egger, in an address to a suburban Boston Chamber of Commerce group Friday, cited the results of a national survey on attitudes toward taxes conducted by the firm of Yankelovich, Skelly & White.

"The challenge of the Yankelovich study," Egger said, "was to delve into the noncomplier personality for clues. Why do some people comply with tax laws while others do not? A lot rides on our finding the right answers."

Here are some of the findings, as reported by Egger: Four of five taxpayers believe the current tax system benefits the rich and is unfair to the ordinary working man or woman. Almost one person in five (19 percent) admits to cheating on taxes, and, Egger notes, "experts tell us that the incidence of reported tax cheating is probably understated."

* The main reason for tax cheating is that people consider the system unfair.

"This survey clearly indicates," Egger said, "that our system is in real trouble. The system is responding to people in similar circumstances in quite dissimilar ways. And people resent a system which gives special privileges to a few, making it more costly and tougher on everybody else."

The Yankelovich report has not been released, and Egger mentioned only the top of the findings. A Treasury Department spokesman said the survey was not available as the Regan plan was being formulated, but angry testimony at public hearings earlier in the year was.

Regan's report and Egger's speech both focus on grotesque use of loopholes.

Regan's report to the president noted that in 1983, according to treasury estimates, 9,000 people with "incomes of $250,000 or more paid no tax as a direct result" of tax shelters. And, 59,000 at the same income levels were able to reduce tax payments by at least half.

"The Treasury Department's recommendation," Regan writes, "reflects the broad political consensus of the American people that the present system is too complicated and favors special interests at the expense of the general public."

Of course, just because the Treasury secretary says his plan is aimed at making the tax system fairer to the average citizen and family does not mean that it would. Tax revisers always say their plans are fairer. As economist Walter Heller put it: "Those whose taxes would be equalized upward in this process are understandably apprehensive. And they are puzzled at the prospect of the Reagan White House and the Regan Treasury storming the citadels of tax privilege and power."

At this point, there is real doubt that the president does want to storm those citadels but little doubt about Regan's sincerity.

"Fundamental reform of the tax system is required to correct the problems," Regan's report notes. "The tax system must be made simpler, more economically neutral, fairer and more conducive to economic growth."

Repeatedly the report refers to deterioration of taxpayer morale, and Regan addresses the subject, concluding that, despite the "controversial" nature of the plan, "a far greater number of Americans will benefit from the suggested rate reduction and simplification."