Another round of increases in the minimum and maximum standard deductions for all classes of taxpayers makes it important to check the alternatives carefully before deciding whether to itemize deductions.

Generally it will now pay to itemize only if you're a homeowner or have large deductions of a special nature such as alimony, medical payments, business expenses, or a casualty loss. The table accompany this article shows the breakeven points - the amount of deductions for each filing category at which it becomes advantageous to itemize.

You need not itemize this year in order to claim a deduction for child care; this has been converted to a tax credit for 1976. And for 1977 and later years, you will be able to claim a deduction for alimony paid without itemizing.

The standard deduction for 1976 and following tax years is 16 per cent of adjusted gross income with a minimum of $2,100 and a maximum of $2,800 for joint returns or a surviving spouse, minimum of $1,050 and ceiling of $1,400 for a married taxpayer filing separately, and $1,700 to $2,400 for all others.

TAX TIP: If you decide to itemize, you should be able to support every deduction with a receipt, cancelled check, or similar evidence. However, claim every deduction which you honestly believe qualifies even if you don't have documentary proof of payment.

If your return is audited and a deduction is questioned, allowance of an unsubstantiated deduction will be a matter of judgement on the part of the IRS examiner.

As a general rule, medical expenses may be deducted only to the extent that they exceed 3 per cent of adjusted gross income (line 15c of Form 1040). Expenses for medicines and drugs are limited further: You first must deduct 1 per cent of adjusted gross income, then include the balance with other medical expenses.

There is one exception. Half of your medical insurance premiums up to a maximum of $150 may be deducted without regard to the 3 per cent limitation; the balance then should be added to other medical costs.

You may count your own medical expenses (and those of your spouse on a joint return) plus qualifying expenses paid by you on behalf of all dependents claimed on the return - including a dependent you claim as the result of a multiple support agreement.