President Carter's tax cut proposals would reduce almost to zero the tax liability of a typical family of four with an income of $10,000 a year or lower. But they would have only a small effect on higher income brackets; the tax cut for a family of four with an income of $35,000 a year would be only about $70, experts calculated yesterday.
Carter's proposals would also have uneven effects on corporations, experts said.
One of his recommendations would let corporations wipe out up to 90 per cent of their tax liability each year by means of the tax credit for investment. Currently they can use it to lower their liability by 50 per cent.
A 90 per cent credit would be of particular benefit, experts said, to airlines, railroads and utilities, in part because they have such high capital costs; the credit allows a company to reduce its taxes owed by 10 per cent of the cost of new equipment and under a proposed Carter modification - the cost of new structures as well.
But analysts said the corporate tax changes Carter is recommending would probably not so greatly benefit other industries in need of help, such as steel and chemicals.
For individuals, Carter is propsing general reduction in rates of about 2 percentage points across the board, plus two other changes.
Under the first of these, the familiar $750 personal exemption that every taxpayer is allowed for himself and each dependent would be replaced by a $250 credit. The credit would be subtracted directly from taxes owed, rather than from taxable income as exemptions are. Thus the credit would be of the same dollar value to taxpayers in all brackets, while an exemption is worth more to those in higher brackets.
The rate reductions, experts said, would be worth several hundred dollars to a family at the $35,000 income level, but less than $50 to a fmaily at th $10,000 level.
A shift from $750 personal exemption to $250 credit, on the other hand, would lower the taxes of the $10,000 family of four by $294, compared to present law, the experts said, while raising the taxes of the $35,000 family by $291.
Thus for the family in the higher bracket, the gain from rate reduction would be offset by the shift from exemption to credit. That family also would lose a little under Carter's proposal to drop the deductions allowed for state and local sales and gasoline taxes.
Experts said a typical family of four making $10,000 a year now pays a tax of $446. Carter's plan would reduce this to $16. The family making $35,000, however, would still pay about $6,148 - only about $70 less than now.
The experts cautioned that these calculations could change somewhat, depending on the fine print in the eventual Carter proposal.
They also said Carter's plan would be likely to have a greater effect on married couples with children than on single individuals, because of the conversion from exemption to credit. The more persons listed on a tax return, the greater the effect of this conversion on the taxes owed. That is true whether the conversion would raise those taxes or lower them.
Carter's proposed cut in the corporate tax rate alone would mean about $4 billion in tax savings to companies during the next 2 1/2 years, often netting millions of dollars for individual large firms.
The proposed extension of the present 10 per cent investment tax credit to cover outlays for new industrial buildings is designed to spur lagging capital investment in this area.
However, economists point out that this extension would benefit primarily so-called "labor-intensive" industries, such as textile manufacturing, where extra workspace is a major part of investment. The industries most in trouble, such as steel, would get relatively little break; in the steel industry, analysts say, the bulk of the investment outlays are for equipment, not structures.
Finally, Carter has proposed allowing companies to use the investment credit to offset 90 per cent of their taxes, rather than the 50 per cent limit now in effect.
This essentially would prevent airlines, railroads and utilities from losing most of a special, temporary 100 per cent writeoff capability that Congress gave them last year. The 1976 provisions were scheduled to be phased out over the next couple of years.
For other industries, however, it would have little major impact, according to analysts. Economists point out that the writeoff is valuable only to firms having high investment costs and low earnings.