One of the biggest criticisms leveled at the nation's tax code in recent years has been that it's riddled with special deductions and tax credit that complicate the law unnecessarily.

When the government wants to encourage taxpayers to contribute to worthy causes, it provides a tax deduction for donations to charities. The measures may work, but it adds to the complexity of filling out a tax return. Put all these special breaks a morass.

These special deductions have become a target of tax "reformers" lately. Liberals complain that the code is being pushed beyond its original purpose - to levy and collect taxes. Instead, it's been turned into a system of incentives designed to influence the way people act and conduct their business.

It was just this trend toward complexity that President Carter attacked during the 1976 presidential campaign. The tax code was so full of special credits and exemptions, Carter told fundaising audiences, that it had become "a disgrace to the human race." He promised to end many of these breaks.

So, in reviewing tax developments during 1977, it might be worthwhile to look not just at efforts to "reform" existing law, but also at proposals that would tend to complicate the tax code further. And in that category, one man stands at the year's biggest tax complicator. His name, ironically: Jimmy Carter.

Although Carter campaigned vigorously on a plank to abolish special credits and deductions, he's proposed enough this year to boggle the mind of any tax purist. (The President has been planning a massive set of proposals to end the biggest special tax breaks, but has pared that back inthe face of opposition.)

The first came as part of his January economic stimulus package. The rest were included in the April Carter energy provisions. But the President has proposed other tax complicators as well.

The list includes these credits or deductions:

A special "payroll tax credit" in the January economic stimulus package, designed to encourage employers to hire more workers. The proposal would have allowed companies to subtract from their income taxes and amount equal to 4 per cent of their shares of employer' payroll taxes.

A "home insulation tax credit," included in the Carter energy program, that would allow homeowners to reduce their taxes by up to 25 per cent of the first $800 and 15 per cent of the next $1,400 they spend on energy conservation measures - at a time when insulation sales already are outstripping supplies!

A "business conservation credit," also in the energy bill, that would allow companies an additional 10 per cent investment tax credit for spending on energy conservation measures - including solar-power equipment for industrial and commercial purposes.

A "cogeneration tax credit" allowing business an addiitonal 10 per cent in investment tax creidts for investment in equipment that enables them to produce electric power and other forms of energy - such as heat or process steam - from the same facility.

A "solar tax credit," designed to encourage conversion to solar hearing - enabling taxpayers to reduce their tax bills by up to 40 per cent of the first $1,000 they spend and 25 per cent of the next $6,400, to a maximum credit of $2,000. The size of the writeoff would decline in late years.

Moreover, Carter also is expected to proposed a new credit for working spouses in his tax package in January. And the more comprehensive proposal the President was considering in September, but later scrapped, contained a fiercely double taxation of corporate income.

Not all these proposals have made it as is into the nation's tax code. The payroll credit proposal, for example, was transformed by Congress into an even more complex "jobs credit." The Internal Revenue Service issued new regulations on that last week - 2 1/2 pages in small, legal-sized type.

The energy measures still are stalled in a House-Senate conference committe. But many of them - or simialr versions - are expected to be enacted into law, and Congress even has added a few new credits of its own, to help complicate the law a bit further.

To be sure, they may be some arguments that at least a few of the new payroll and energy credits were needed. The payroll credit came in response to criticism that the rest of the Carter stimulus package wouldn't have done much to spur new jobs. The energy proposals were more dubious, but mixed.

Moreover, the administration has done a few things this year to simplify the plight of taxpayers. Carter, for example, accepted congressional changes passed last spring which simplified preparation of income tax returns by combining the personal exemption and standard deductions into a single tax table.

And the IRS has overhauled its tax return forms 1040 and 1040A to make them easier to fill out. Even the instruction booklet is written a bit more simply (although inexplicably, the IRS needed two separate private consultants to help put its forms into English).

Still, for a man who won the election in part by promising to eliminate all those credits and to cut taxes for individuals. Jimmy Carter isn't ending 1977 with very much to brag about. Which all goes to reinforce the President's admission last fall that dealing with the tax code is proving more complicated than he thought.