By the time you reach this final column you should have your federal tax return ready to go. If you owe Uncle Sam some additional money, you're not in any hurry; on the other hand, if you have a refund coming, your're probably anxious to get the return in the mail.

But don't turn it loose yet. The information required on the state tax returns for the District of Columbia, Maryland and Virginia is derived almost entirely from the federal return.

And sometimes the additional research you do for the state return will trigger a change on the federal return. So complete your federal return first, then use if as a basis for working on the state return.

The tables with this article provide the basic filing instructions for each of the three local jurisdictions. Note that Maryland filing requirements are the same as federal; but the District and Virginia have lower dollar minimums than the IRS.

You should file for a refund if taxes were withheld from your pay, even if your income is below the miniumum for your filing status. If you live in the District and are not otherwise required to file a return, you may request a refund of taxes withheld on Form D-40b.

None of the three local tax departments will compute your tax liability for you; you must do all the calculations yourself. In all three jurisdictions you may round your figures to whole dollars as you did on the federal return.

Use the "peel-off" label from the instruction booklet on District or Virginia returns making any necessary corrections. Use the Maryland label only if all the information is correct.

All three states provide a tax benefit for a married couple (living together) when each spouse has separate income. Whether to file a joint return or combined separate returns (on the same form) depends on the amount of income attributable individually to each spouse.

The District, Maryland and Virginia all offer the following four categories for filing:

Single (unmarried, widowed before 1979, divorced or separated.)

Married, filing separately (mandatory in Maryland if you filed separate federal returns).

Married, filing jointly (in Maryland and Virginia, only if you filed a joint federal return or were not required to file a federal return).

Married, filing combined separate returns (in Maryland, only if you filed a joint federal return and elect to file separate state returns).

The District has a fifth filing category: You may file as "head of family" and take an extra personal exemption if during 1979:

You were single or married but not living with your spouse; and

You home was also the home of a person who qualifies and is claimed as a dependent on your D.C. return. Exemptions

In D.C. personal exemptions are the same as on the federal return: one per taxpayer (and spouse on a joint return) plus one for age 65+, plus one for legal blindness. Exception: If you file as head of family, you get an extra personal exemption (not true on the federal return).

One exemption is allowed for each dependent claimed on your federal return. The District allowance is $750 for each exemption for a full year; or $62.50 per month on a part-year return.

Maryland residents claim $800 per exemption, or $66.67 a month for less than the full year. You are entitled to one exemption for each exemption (personal and dependent) claimed on the federal return.

In addition, on the Maryland return you get an additional exemption for each dependent who has reached the age of 65. But the additional exemption for blindness is only allowed for the taxpayer and spouse.

If you are a Virginia resident, the number of exemptions -- each worth $600 a year -- is the same as on the federal return. But in addition to the normal extra exemption for age, there is further $400 allowance for each taxpayer (but not dependent) who was 65 or older on Dec. 31, 1979. Income

In Maryland and Virginia, you start with the income you showed on the federal return, then make some modifications -- both up and down -- to arrive at the amount of income taxed by the state.

The District requires that you modify your federal income to fit D.C. requirements first, then enter the proper D.C. income by categories on page 2 of Form D-40.

Here are the major differences between federal and state rules on reporting income.

DC.: The federal dividend exclusion is not authorized; you must show the gross amount of taxable dividends received. But exclude interest received on obligations of the U.S. government or any federal agency. And the District does not tax interest on bonds or other obligations of any other state or muncipality.

A state tax refund shown as income on the federal return should be excluded. And deduct any unemployment compensation included as income on your federal return; such payments are not taxable by the District.

A reduction of salary made, by agreement with you employer, to purchase a tax-sheltered annuity may not be excluded from gross wages for D.C. If not included in wages on your W-2, you must add it.

There are major differences between federal and D.C. handling of income from a pension to which you contributed. You should report as income each year three percent of the total amount equal to your contribution. From then on, the entire amount received is taxable as ordinary income.

Maryland: Add to federal income any interest received on obligations of state and local governments other than Maryland. And add back in the dividened exclusion allowed on the federal return.

For Maryland tax purposes, substract from federal income interest on U.S. obligations and any state tax refund reported as income on your federal return. Also exclude -- to the extent it was included in federal income -- any capital gain realized on the sale of bonds issued by the State of Maryland or any political subdivision.

Maryland allows exclusion of up to $5,700 of pension income if you were 65 or older or totally disabled on Dec. 31, 1979 -- but reduced by any Social Security or Railroad Retirement benefits received.

Virginia: There are very few changes required to adjust federal income for state tax purposes. You need only add to federal income any interest received on bonds or other obligations issued by other states.

Then subtract interest received on federal obligations, and any state tax refund reported on your federal return. If you receive retirement income from the State of Virginia or its agencies or from any county, city or other subdivision, the entire amount of such income is excludable. Adjustments to Income

D.C.: The District allows the same federal adjustment for employe business expenses, alimony payments and the disability income exclusion. But no adjustment is authorized for payments to either an IRA or Keogh retirement plan.

Moving expenses may be claimed as an itemized deduction on your D.C. return, not as an adjustment. But you may claim only expenses equal to the amount of any reimbursement (from you employer) which is included in income.

Maryland: On your Maryland tax return you may claim all of the adjustments taken on your federal tax return, and to the same extent.

In addition, the Maryland tax benefit for dependent care expenses is an adjustment to income rather than a tax credit. Subtract from income an amount equal to five times the amount of the federal tax credit taken.

Virginia: The State of Virginia allows all of the same adjustments you had claimed on the federal return, without modification. Deductions

In each of the three local jurisdictions the standard deduction is lower than the federal zero bracket amount (ZBA).

D.C.: If you live in the District, you may itemize on your D.C. return regardless of whether you itemized or used the ZBA on the federal return. The deductions for medical expense and for interest may be transferred without change.

(Caution: When computing the deduction for medical expenses, keep in mind that adjusted gross income for D.C. purposes may be different from the federal return.)

You must eliminate any deduction taken on your federal return for state or local income taxes. But the District allows a deduction for gasoline tax; figure 10 cents tax for each gallon purchased during 1979. You also may claim a deduction for a recording tax paid on puchase of a new home in the District.

The deduction for contributions is limited to qualified organizations which carry on a substantial part of their activities in the District. The deduction for contributions cannot exceed 15 percent of D.C. adjusted gross income.

Moving expenses may be claimed as a miscellaneous deduction -- but, as noted earlier, not more than the amount of any reimbursement from your employer which is included in reported income.

Maryland: If you file a Maryland return, you may itemize even if you used the ZBA on your federal return. But in that situation, total itemized deductions may not exceed the ZBA amount.

If you use the standard deduction on a combined separate return, it must be computed on the income of each spouse separately.

Itemized deductions on the Maryland return are the same as on the federal return, except that you must eliminate the deduction for any state or local income taxes.

In addition to the federal deductions, a Maryland taxpayer may be authorized a deduction for the amortized costs of preserving historical structures.

Virginia: Virginia taxpayers may itemize only if they itemized on the federal return. The deductions are the same except for the exclusion of any deduction taken on the federal return for state of local income taxes paid.

Because you only transfer a single figure for deductions for the federal to the state return, be sure to use the total (from line 39 of federal Schedule A) rather than only the "excess" from line 41.

Virginia authorizes a deduction for child and dependent care rather than a tax credit (as on the federal return). Enter five times the amount of the federal credit to get the full allowable deduction. This year the tax benefit is available even if you use the standard deduction. Tax Computation

All three local jurisdictions provide both a tax table and a tax rate schedule. But each state has different qualifying rules and restrictions for use of the table -- so read the instructions for your state carefully.

Maryland has one requirement not found in either the District or Virginia:

After computing the Maryland tax, you must add the local "piggyback" assessment to determine your total tax liability.

The local rate is 50 percent of the state tax in every county (and Baltimore City) except for the following: Calvert, 20 percent; Charles, 45 percent; Queen Anne's, 40 percent; Talbot, 35 percent; and Worchester, 20 percent. Tax Paid to Another State

You may be subjected to dual taxation if you live in one state and have income in another. You may have to file two returns -- one where the income originated, another in your state of residence.

Generally, you will have to pay tax twice on the same income. The District, Maryland and Virginia all have provisions for claming credit for taxes paid to another state.

The rules in each of the states are different, so check the instructions if this situation applies to you. All three local states require that you attach to your return a copy of the "foreign" tax return to support the credit. Child and Dependent Case

As noted earlier, a resident of Virginia should convert any federal credit for child and dependent care to a deduction -- even if the standard deduction is taken on the state return.

The process is similar in Maryland. The amount of which the federal credit is calculated, rather than the amount of the credit itself, is allowed as a substraction modification to federal adjusted gross income.

The District, however, provides for a tax credit similar to that authorized on the federal return. Although the allowable expenses are essentially the same, the D.C. credit is limited to 6 percent of those expenses, not the 20 percent permitted by federal rules. Political Contributions

The District allows a credit for campaign contributions made to specified political candidates. The list of those offices for which contributions are deductible is found on page 4 to the instruction booklet.

This D.C. credit for political contributions is 50 percent of qualifying payments up to a maximum credit of $50 on a joint return or $25 per taxpayer on all others.

Maryland and Virginia do not permit a credit of any kind for political contributions, but Maryland makes provision on its tax form for each taxpayer to contribute $2 voluntarily to the State Fair Campaign Financing Fund. If you elect his payment, the two dollars must be added to your normal tax liability. Property Tax Credit

Residents of the District with Household gross income of $20,000 or less during 1979 may be eligible for a property tax credit. The requirements to qualify are on page 7 of the D.C. tax instruction booklet.

The credit is claimed on Schedule H. If you file a D.C. income tax return, take the credit on line 19 of Form D-40, and attach Schedule H to the return.

You still can claim the property tax credit even if you do not file a D.C. income tax return. File Schedule H by itself, and if you qualify you will receive a cash payment for the amount of the credit.

Maryland does not offer a property tax credit as a part of the income tax system. But this year an application for the Maryland homeowners' property tax credit (Form HTC-60) is included in the instruction booklet.

Do not attach Form HTC-60 to your Maryland income tax return, and do not forward it in the same envelope with the tax return. Two seperate envelopes are included in the instruction booklet -- one for you income tax return, the other for mailing the homeowners' tax credit application.

There is a Maryland personal property tax credit available on the income tax return -- but it applies only to state personal property tax paid on property used in a trade or business.

If you are eligible for this credit, use Maryland Form 502-CR; and include the amount of the tax (for which credit is claimed) in Schedule C of Form 502, as an addition to federal adjusted gross income. Tax Credit for Elderly

A Virginia resident may qualify for a special tax credit if he or she was at least 62 years old on Dec. 31, 1979, had adjusted gross income of less than $15,320 and had less than a specified amount of Social Security or Railroad Retirement Act benefits.

The credit base for each age group and the instructions for claiming the credit are found in Part VII of Virginia Form 760. Additional information and detailed qualifying rules are on page 8 of the tax instruction booklet.