President Reagan's tax reduction plan has run into so much trouble on Capitol Hill that an alternative has now been proposed.

Several alert Democrats have discovered that an across-the-board 10 percent cut would save some people more than it would save others.

For example, the Democrats charge that a 10 percent cut would save $10,000 for a rich man who otherwise would have to pay $100,000 in federal income tax, whereas a poor fellow who now pays $100 would save only $10!

"This country obviously isn't going to stand for such scandalous discrimination," said Rep. Smoldering J. Hemp as he introduced a measure to reverse the across-the-board concept. "The poor man who now pays $100 ought to get the $10,000 tax savings. The rich man who pays $100,000 can afford to get along with a $10 saving."

Hemp said he cannot abide some people saving more than others. "It's all right for some to save less, if they pay more, it's not all right for others to save less, if they don't," he explained.

Sen. Waxing V. Wroth, cosponsor of the measure, said, "The American way is to set higher tax rates for the rich than for the poor. This may seem unfair, but we make up for it by giving bigger tax reductions to the poor than to the rich.

Key Democrats in the House have been reported to be alarmed about rumors that rich people have more income than poor people.The General Accounting Office has been asked to investigate.

Concern has also been expressed that although the rich are permitted to enjoy the status of paying a top federal income tax rate of 70 percent plus top rates on their state and local income taxes as well, they sometimes have a little money left over that the government doesn't get. There is talk of reviving the Un-American Activities Committee to look into this.

One Democratic committee chairman who declined to be identified told this column, "I don't mind letting people with higher incomes pay a higher percentage of tax, but it would be unforgivable if we were to let them have the same percentages of tax reduction as the poor. Where's the equality in that, where's the justice?"

The Hemp-Wroth tax proposal will go before 10 percent of the committee on Wednesday, or 20 percent if unmarried or head of household, exclusive of ground rents, royalties, depreciation or the Railroad Retirement Act.

Doesn't it restore your faith in the democratic process to know that your tax liability is being determined by such sensible people?