A new Brookings Institution study yesterday proposed a sweeping overhaul of the nation's tax system that would slash tax rates drastically - and distribute the tax burden more evenly - by eliminating most deductions.

The document, compiled by a group of leading tax experts, call for broadening the tax base by taxing many forms of income that now are exempt - such as interest, employee fringe benefits and some capital gains - and ending most existing deductions.

The study shows these changes would yield so much in new revenues that tax rates could be pared from the present 14 to 70 per cent range to new brackets of between 10 and 44 per cent, with an increase in the personal exemption.

The proposal parallels in theory the tax-revision package now being drafted by the Carter administration, but goes substantially farther than the President is expected to venture in reshuffling the tax system.

Joseph A. Pechman, editor of the 311-page volume conceded that, in view of political realities, none of the tax experts who helped prepare the study "believes you can achieve this kind" of sweeping overhaul in one piece of legislation.

However, he said the institution published the proposal to provide "a gauge" against which to measure the upcoming Carter package. "You can see how far it goes," he said, referring to the President's proposal.

Among the now-exempt income the Brookings plan would tax are half of long-term capital gains, dividends, interest on state and local securities, employee fringe benefits, Social Security and veterans' benefits and profits from the sale of a home.

It also would eliminate or restrict a number of existing deductions, including home mortgage interest, interest paid on loans state and local taxes and most medical and dental expenses, possibly above a floor of 5 per cent.

The Brookings study showed that without any changes in present tax rates a reshuffling of that magnitude would bring in some $118.2 billion in added revenues - far more than the government needs, even if it wanted to climinate the deficit.

As a result, it said, taxes could be cut significantly, both by raising the personal exemption for all taxpayers and by reducing tax rates to between 10 and 44 per cent - an average slice of more than one-third.

In descussing the proposal, Pechman said the plan would provide substantial tax relief to most taxpayers, particularly those with incomes of $17,000 a year or less, who do not claim large amounts of deductions.

However, he conceded, about 22 million out of the present 100 million persons paying taxes would find their tax bills increased. Most of these, he said, would be persons in upper-mid-dle and high-income brackets who pay less than average now.

Along with other features, the Brookings plan would introduce a relatively new concept - the taxing of "imputed" rent that is the value of the housing a homeowner receives after deducting operating expenses interest and depreciation.

That portion of a homeowner's benefits currently goes untaxed and the householder also receives deductions for interest, taxes and the like. But the Brookings report contends this is "income" just as stock dividends are and should be subject to tax.

Despite the benefits claimed for the Brookings plan, the editors conceded the reshuttling would not resolve some problems interest in the present system:

It would not simplify the tax code which President Carter has called too complex and difficult to follow.

It would not eliminate the disparities in the treatment of single and married persons, including the so-called "marriage penalty" that arises when couples are taxed more heavily than single persons living together.

It would not eliminate doubts about the impact of eliminating preferential treatment for capital gains. Critics warn this step would crimp investment but Pechman argues investors would be satisfied by the offsetting cut in overall tax rates.

The new Brookings study entitled "Comprehensive Income Taxation," was based on a series of papers presented at a conference late last year of 11 nationally-known tax experts, including several who now are working on the Carter tax package.

Included in the group were Emil M. Sunley, Jr., now deputy assistant secretary of the treasury for tax policy, and Donald C. Lubick now Sunley's assistant. Another contributor, James W. Wetzler, is an economist with the congressional JOint Committee on Taxation.