The federal tax forms seem the same and so does the hassle of filling them out. But actually the United States tax system has undergone several major but little-noticed changes in recent years.
The shifts affect individual and corporate taxes and may alter the course of the economy and efforts on Capitol Hill to reduce deficits.
One major shift is that the corporate income tax is providing a much smaller share of federal revenue than it did in the past. In budget year 1964, companies accounted for 20.9 percent of federal revenue. By fiscal 1980, the corporate share was down to 12.5 percent. Last year companies kicked in only 6.2 percent of federal income.
Most experts say the corporate tax is a bad one for a variety of technical reasons and that individuals eventually end up paying all taxes.
But the dwindling corporate tax still may cause problems for business in 1985 when the elections are over and Congress is expected make a major deficit-reducing effort.
The perception that the corporate tax contribution has slipped ''makes us vulnerable'' to attempts to boost corporate taxes, says John M. Albertine, president of the American Business Conference. He notes that while the effective tax rate for all corporations was 16.1 percent in 1982, the fast-growing companies in his organization pay almost double that rate.
The second major change is occurring in the area of individual taxation, where there has been a pronounced shift to consumption-based taxes. Generally, a consumption-based system - of which there are several types - taxes a person on the income spent but not on the portion of income saved.
President Reagan announced in January that the US Treasury Department would conduct a year-long study of the tax system. The Treasury is reviewing several consumption-type taxes, including a tax on consumed income.
But a variety of tax experts say that the US already has taken significant strides toward such a system as the effects of the Economic Recovery Tax Act of 1981 (ERTA) spread through the economy.
The act liberalized the amounts that could be saved, free from current taxation, in individual retirement accounts (IRAs) and Keogh plans. The act also reduced the tax rates on investment income.
''The majority of people now have a consumed income tax,'' says Martin S. Feldstein, chairman of the President's Council of Economic Advisers. ''That is a very fundamental change in the character of our tax system.''
For the individual, a tax on consumed income boosts the incentive to save, because the income put away escapes immediate taxation. For the nation, such a system boosts the amount of savings that are then available for investment by business in new plant and equipment.
Economists disagree on how much consumption-based taxes boost savings. The nonpartisan Congressional Budget Office (CBO) says in a February 1984 report on the federal deficit that the change in savings ''is not likely to be large.''
But the CBO says a consumption tax would have a larger effect on the nation's capital stock beacuse the small gains in savings accumulate over time.
While the US has moved toward a consumption-based individual tax system, economists say such a system has not been completely adopted.
For example, retirement savings in an IRA get consumption-type treatment but savings for the down payment on a home do not.
''You get consumption-type tax treatment of savings if you have the right type of savings,'' says Emil M. Sunley, director of tax analysis at the accounting firm of Deloitte Haskins & Sells. ''But until you have bought a house , you can't save for retirement.''
And limits on IRA contributions mean there is no savings incentive for wealthy individuals, who already save more than the $2,000 annual limit on an individual IRA, according to a study by Brookings Institution economist Harvey Galper.
The favorable effects of moving toward a consumption-type tax will only be felt gradually, Mr. Feldstein notes, because at first individuals move funds from nonshelterd savings into IRA's and other tax-sheltered accounts.
But after a few years, most taxpayers will have exhausted all of their previously accumulated funds. Then they can make additional IRA contributions only if they save more, Feldstein wrote in the President's annual Economic Report.
One sign of this gradual effect is that in 1983 Americans saved only 4.8 percent of disposable income vs. 6.6 percent in 1981.
Experts say that the corporate tax fell as a share of government revenue for a variety of reasons. One reason was that changes in the tax law boosted the size of the tax deductions firms can claim. Then the impact of past oil embargoes and more recently the effects of the recession reduced corporate profits after adjustment for inflation.
In general, tax experts are not sorry to see the corporate tax wane.
''The arguments against the tax - theoretical and practical - are really very strong,'' says Thomas Field, publisher of Tax Notes, an authoritative weekly publication for tax professionals.
Among other things, economists say the corporate tax tends to discourage investment in corporations. At the same time, it encourages companies to finance themselves with debt rather than selling stock, because interest costs are deductible for tax purposes but dividends paid to stockholders are not.