President Reagan would personally save more than $26,000 in taxes if his proposal to overhaul the tax system were enacted, but he would receive an even larger cut from two competing congressional tax-simplification plans.

Reagan's income taxes, which came to $146,353 in 1984, would be cut by more than $52,000 a year under a bill sponsored by Rep. Jack Kemp (R-N.Y.) and Sen. Robert W. Kasten Jr. (R-Wis.), while a Democratic proposal by Sen. Bill Bradley (D-N.J.) and Rep. Richard A. Gephardt (D-Mo.) would give the president a reduction of about $38,000.

Under any of the major tax plans issued in the past year, including the original proposal from the Treasury Department last fall, Reagan's taxes would be lower than under current law.

On the other hand, Vice President Bush would pay higher taxes under both Reagan's plan and the Bradley-Gephardt proposal, while his tax liability would not change if the Kemp-Kasten bill became law.

The estimates come from an analysis of Reagan's and Bush's 1984 taxes by the accounting firm of Touche Ross & Co. at the request of The Washington Post.

The most important factor in lowering the president's taxes would be the reduction in the top tax rate, which is now 50 percent. Lowering the top rate is more important in reducing the president's tax bill than the curtailment or elimination of deductions, which all the proposals would do to varying degrees.

The changes that the various proposals would make in the taxes owed by Reagan and Bush do not necessarily represent how the plans would affect other taxpayers.

The Treasury says 58 percent of Americans would receive a tax cut under the administration's plan, 21 percent would see no change in their taxes and 21 percent would pay more.

Only the Reagan proposal is technically under consideration by the congressional tax-writing committees. But elements of the others probably will be proposed as amendments or changes when the House Ways and Means Committee and the Senate Finance Committee begin drafting a bill in the fall.

Under the Reagan plan, the lowest- and highest-income taxpayers would receive the largest cuts, in terms of percentages. Those with annual incomes of more than $200,000 would receive a tax cut of 10.7 percent, according to the document explaining the details of the Reagan plan.

Touche Ross, using somewhat different calculations of income, estimates that people with taxable income of $200,000 or more would see their taxes reduced about 25 percent.

Reagan falls into that income category. Unlike some wealthy taxpayers, however, the president does not rely heavily on deductions to shelter his income. Last year, he paid 33.6 percent of his adjusted gross income in federal income taxes.

Reagan, who files a joint tax return with First Lady Nancy Reagan, would pay $26,942, 18.4 percent, less in taxes under his proposal, which has a top rate of 35 percent, than he would under current tax laws.

Reagan's tax payment would be $119,411, compared with a tax liability under current law of $146,353 after a statistical adjustment that applies tax brackets effective in 1986 to Reagan's 1984 income. Touche Ross made the adjustment so that all the tax plans would be figured for the same base year.

For the same reason, the accountants assumed all the plans were fully in effect, even though some include transition periods for rate reduction and limitations on deductions.

Under the Bradley-Gephardt plan, which has a top tax rate of 30 percent, Reagan's tax bill would be $108,239, a cut of 26 percent. The Kemp-Kasten bill has a flat rate of 24 percent and would cut the president's taxes to $94,023, a reduction of 35.8 percent.

The smallest tax cut for the president would come from his Treasury Department's original revision proposal, which would cut his taxes by 17.1 percent to $121,254, according to the Touche Ross compilations.

The top rate in that plan is 35 percent, the same as in the current administration proposal, but the Treasury proposal would limit more deductions.

Bush would not see his taxes cut by any of the major tax plans, and two of the proposals would increase his tax bill. Bush and his wife, Barbara, had relatively small tax liabilities for 1984 and were obliged to pay under the minimum-tax provisions of the tax code.

Bradley-Gephardt would curb Bush's large deductions the most, raising his tax bill from $11,735 to $19,395, 65.3 percent. The Reagan plan would increase Bush's tax bill to $13,934, 18.7 percent. Because the other two plans wouldn't alter the minimum tax -- the original Treasury proposal, nicknamed "Treasury I," would get rid of it but not until 1990 -- Bush's tax bill would not change under Treasury I or Kemp-Kasten.

Reagan also would benefit because several of the deductions he took advantage of in 1984 would be retained under the proposals.

The president's tax-simplification plan would remove only one of his large deductions: He would lose $34,114 in write-offs for state and local income, property and sales taxes. Other deductions, such as $42,128 in legal fees and other miscellaneous expenses, would be curtailed but not eliminated.

Reagan would lose $4,409 of that writeoff because his tax plan would limit the deduction to the amount by which it exceeded 1 percent of adjusted gross income. Other Americans use that deduction for such expenses as professional fees and union dues.

The president could retain a number of deductions, including $20,616 in charitable contributions, under his plan.

Reagan also could keep $4,870 in interest deductions on the mortgage on his California ranch. His other interest deductions are small enough that none of the plans cut them back by much.

Reagan's tax payments would be greater under Treasury I than under his plan, mostly because Treasury I would limit the deductibility of charitable contributions.

Under Bradley-Gephardt, all deductions are taken against the bottom rate of 14 percent, rather than the taxpayer's actual tax bracket. A deduction under current law saves taxpayers in the highest bracket 50 cents on the dollar, while under Bradley-Gephardt a deduction would be worth only 14 cents on the dollar.

Some wrinkles in the way the Kemp-Kasten plan calculates taxable income mitigate the effect of the flat 24 percent tax rate. The actual rate a taxpayer pays can vary from 19.2 percent for low-income taxpayers to 28.8 percent for high-income taxpayers. Even with those provisions, the low rate ultimately makes this the best bargain for someone in the president's tax situation.

Bush presents a more unusual case, the Touche Ross accountants said. He had two large deductions in 1984 that significantly reduced his tax liability: a $54,671 interest payment to the Internal Revenue Service related to back taxes for 1981 and a $41,000 loss on an apartment building in Houston, which as part owners the Bushes sold but had to foreclose on when the buyer couldn't keep up the payments.

Those deductions left the vice president with no taxable income in 1984 (he had a net loss) and thus subjected him to the existing minimum tax, which effectively enlarges taxable income by reducing the types of deductions than can be taken.

Only Bradley-Gephardt would restrict the deduction of the interest payment to any substantial degree, raising Bush's taxable income, the income on which the tax rate is assessed, from zero to $75,233 (Bush's adjusted gross income in 1984 was $87,239).

Under the Reagan plan, Bush would lose a state-and-local tax deduction of $3,816, but his taxable income would still be low enough to require him to pay the 20 percent minimum tax.

The amount he would pay would be $13,934 rather than the $11,735 he would pay under the regular minimum tax (which is retained fully in Kemp-Kasten and retained for five years in Treasury I) because the Reagan plan would strengthen the minimum tax from what it is now.