I find Mayor Marion Barry's proposed income tax increase unconscionable. Any increase in the individual income tax would be detrimental to the well-being of the District's citizens.

Just last year the D.C. Council reformed the tax law by substantially reducing the number of people subject to the individual income tax and provided much needed relief to taxpaying residents. These measures were enacted even though the mayor had requested a $25.7 million income tax increase for fiscal year 1987. But the mayor did not get his tax increase, the government continued to function, and the District ended the year with more than $20 million in unspent revenues that were used to help retire a portion of the deficit.

I believe the same can and must be done this fiscal year and next.

The mayor is proposing to increase spending by $58.1 million this fiscal year and by another $166.9 million in the next. In addition, the 1989 budget would create 1,124 new District government jobs. To fund these increases, the mayor has proposed an income tax increase of $220.8 million through fiscal year 1993 -- $15.9 million this fiscal year and $46.7 million the next.

The mayor proposes to: 1) increase the individual income tax rate for taxable incomes above $20,000 from 9.5 percent to 10 percent; 2) repeal an increase in the personal exemption; what was to have been an exemption of $1,370 by 1991 will drop back to $885; 3) impose a 5 percent surtax on the individual income tax in 1989.

What these increases would mean for District residents depends on the income and deductions of each individual. But some broad conclusions can be drawn. For example, a married couple with two children would normally claim four personal exemptions. If the personal exemption is reduced to $885, that family would have $560 more income subject to tax in 1988, and $1,940 more income subject to tax in 1991. Heads of households, persons over 65 years of age, the blind and the disabled would suffer a double increase because they are entitled to an additional personal exemption.

The combined impact of the reduction in the personal exemption and the increase in the tax rate would be particularly onerous this year. The reason is that, since January, District withholding has been based on the higher personal exemption and a top tax rate of 9.5 percent. If the mayor's tax increase is adopted, this withholding would not change until the end of the year. Residents filing their 1988 returns would find that they had been underwithheld, and many would have to make payments they had not anticipated making.

Taxpayers who managed to survive this 1988 tax increase would then find that they faced not only more increases in 1989 but also a 5 percent surtax on the income tax they owe. While the mayor says he wants this surtax for one year only, I have yet to see a tax that, once enacted, lasts only one year. The fear is that the surtax would be extended year by year, as the mayor identifies additional spending needs.

These increases are not being requested because of a "shortfall" or reduction in the District's tax base. Rather, current estimates are that revenues from the individual income tax will increase in this fiscal year by $23.9 million over the original estimates, with additional increases of $38.4 million in fiscal 1989, $37.8 million in 1990, $49.7 million in 1991, $57.9 million in 1992, and $60.1 million in 1993. This means that from fiscal years 1988 through 1993 the District can expect additional revenues from the individual income tax of $267.8 million without the tax increase proposed by the mayor.

Recent Census Bureau figures reveal that the District has the second highest per-capita tax burden in the nation, exceeded only by the state of Alaska. This state of affairs cannot be allowed to continue.

So, budget time at the District Building finds me singing the same tune I sang last year and which I've been singing for the past 13 years: taxes must be reduced, not increased.

Maybe if I sing long enough, the mayor will learn the tune. -- John A. Wilson is a member of the D.C. Council.