For some people, this year Santa Claus may be none other than Uncle Sam.

That's because tax laws in some cases make buying a personal computer for a business or trade more attractive than waiting until next year.

All that's required is that:

* You pay for and have the computer in place and in use no later than midnight Dec. 31, 1982.

* You use it for business or trade purposes, or as an aid in the production of income.

* And you're certain that you'll be able to convince the tax collectors of that should they decide to question your deduction.

If your computer will be used for business purposes, you basically have two different tax options.

You can take a one-time tax write-off of the cost of the computer up to a maximum of $5,000 this year, deducting the cost of the computer from your income. The ceiling rises to $7,500 next year and $10,000 the year after, but $5,000 is more than most first-time computer buyers will spend.

Or you can both take a 10 percent investment tax credit on this year's taxes and depreciate the cost of the computer over a five-year period, counting 1982 as the beginning of the period of depreciation.

Essentially, the 10 percent investment tax credit enables you to take 10 percent of the computer's purchase price right off the top of your tax liability. At the same time, the year's accelerated depreciation is deducted from your taxable income.

"The big thing is the investment tax credit of 10 percent," said Barry Goodman, a tax specialist in the CPA firm of Leopold & Linowes in Washington. "It'll be there next year, but it won't be allocated on the whole amount of the computer's purchase price" because of impending changes in the tax law.

Goodman explained that the investment tax credit will lose some of its "umph" if you wait until next year, because the value of the computer for tax purposes will be reduced in future years whenever the tax credit is used.

The tax people have figured out that giving a 10 percent tax credit and allowing you to depreciate the entire cost of the computer (or other business equipment) amounts to double dipping. In effect you're claiming depreciation on the 10 percent of the cost that the government has already given you back through the tax credit.

They're closing that loophole in 1983, but it's open until Dec. 31.

Thus, beginning next year, a $1,000 computer, which will net a $100 tax credit, will be valued for depreciation purposes at $1,000 minus one half of $100 (or $50). You would be able to depreciate only $950 over five years.

"And, if you [buy the computer] this year, you get the 10 percent back as soon as you file your taxes. If you wait [until next year], you don't get it back until 1984," Goodman noted.

In addition, buying a computer this year is somewhat more attractive because President Reagan's 10 percent tax cut will reduce the value of using the accelerated depreciation approach. The tax cut could mean that next year you will find yourself in a lower tax bracket, so that the same tax deductions that could lower your tax liability this year may not have as much potential for savings next year.

Goodman also said that, in some cases, you might be able to take advantage of the 10 percent investment tax credit if you are leasing your equipment. But because the laws are more complicated in such instances, he advises that you consult your tax adviser before leasing a computer with that in mind.

The choice between expensing the computer in one year and claiming the tax credit and depreciation depends on your personal finances, your tax bracket this year and in the years ahead.

If you're in the top tax bracket -- paying a 50 percent rate -- you can recover half your purchase price as soon as you file your Form 1040. Depreciating the investment can produce bigger tax savings in the long run. The best tool for making the comparison is your brand new computer.

If you buy a personal computer for managing your financial portfolio, "you'll probably have to do some arguing" with the taxman, Goodman says. "But it's worth trying if you really do spend time using it for that purpose."

But you must be prepared to show that it was necessary for you to purchase it and that you used it a "reasonable amount of time" for the purpose you say you did. One way to do that is to keep a log -- in the computer -- of what it's being used for.

"You had to purchase it with the idea in mind that it will aid you in the production of income, like in real estate or financial management," Goodman said.

Showing the tax people you've purchased sophisticated financial management software -- a stock portfolio system or a specialized commodity trading program -- will help make your case that the computer is used for profit-making purposes.

But don't try claiming game cartridges or a pair of joy sticks as a tax deductible business expense.