How would candidates wield tax-cut shears?

As Jimmy Carter and Ronald Reagan hit the fall hustings, no subject is likely to be more urgently debated -- or more intently listened to by voters -- than taxes.

Unless the law is changed, millions of American families will pay sharply higher taxes next year, both in social security and income levies.

The maximum payroll, or social security, tax rises from $1,587.67 this year to $1,975.05 in 1981, an extra bite of $387.38 on Americans earning $29,700 or more.

All workers will pay more than they do this year, for the tax rate also climbs -- from 6.13 percent of taxable income to 6.65 percent in 1981.

Two-income families will be especially hard hit, since both husband and wife pay social security taxes on their wages.

A great many families, in addition, will be saddled with higher income taxes, as wage boosts designed to offset inflation push them into higher tax brackets, a phenomenon known as "bracket creep."

The net result, for many millions of Americans, will be less money left over to spend on goods and services, because of inflation and higher taxes.

What to do about this is emerging as a key point of contention between President Carter and Republican challenger Reagan.

Mr. Reagan's response is to aim a clear, uncluttered message to voters, with particular appeal to middle- and upper-income Americans.

Reagan wants a 10 percent across-the-board income tax cut next year, to be followed by reductions of equal size in 1982 and 1983. This would bring tax rates from the present range of 14 to 70 percent down to a range of 10 to 50 percent.

With these reductions in hand, Reagan would institute a permanent, annual adjustment of taxes, to prevent inflation from pushing people into higher brackets.

Such a program may prove to have great appea. A key Reagan adviser claims that anyone paying $2,000 or more in income taxes would benefit more from the Reagan formula than by any tax plan yet disclosed by the White House.

Reagan aides say this would embrace a broad range of taxpayers, including many "blue collar" families, especially those earning two incomes.

With no program of his own ready for unveiling, Mr. Carter attacks the Reagan plan on two grounds -- equity and inflation:

* This "soak the poor" tax cut program, says Carter, would provide upper-bracket taxpayers with "tax breaks up to 35 times greater than those allowed middle-income wage earners."

A person paying $10,000 in income taxes, for example, would get a $1,000 reduction, compared with only $100 for someone paying a $1,000 tax.

* the Kemp-Roth tax plan, from which Reagan's program is drawn, is described by the President as perhaps the "most inflationary piece of legislation ever introduced and seriously considered by the US Congress."

(The authors of the plan are Sen. William V. Roth jr. [R] of Delaware and Rep. Jack F. Kemp [R] of New York.)

An income tax cut of the Reagan variety, according to White House officials, would feed inflation by pumping fresh consumer spending into the economy, without enhancing the nation's long-term potential to produce goods and services.

Adherents of Reagan-Kemp-roth contend that their tax cuts would so stimulate the economy that revenues would outweigh costs, the jobless rate would drop, and inflationary effects would be offset, if cuts were made in government spending.

Lack of a Carter counterprogram, according to White House officials, reflects their view that a tax plan, to be effective, should be carefully worked out and targeted to achieve certain results.

They oppose efforts to whip up a tax cut program in the heat of an election campaign, though they concede the President may be forced in this direction, if the Reagan proposal appears to catch fire.