Marylanders who have savings accounts or do volunteer work are among those who may benefit this year from changes in the state's 1980 income tax law, according to state Comptroller Louis T. Goldstein.

Married couples may claim $400 in tax-free interest income if they earn interest on savings or investments; while single taxpayers may claim up to $200 in tax-free interest. State taxpayers do not have to itemize on the Maryland return to take advantage of the change, but they must file the "long" form 502.

Those who use their own vehicles to perform volunteer services for certain nonprofit organizations will be able to subtract up to 20 cents per mile from their incomes on the 1980 state return, depending on the extent of an reimbursement of transportation expenses.

Contributors to 1980 political campaigns may subtract half their donations -- up to $50 -- from taxable income.Married couples may subtract a maximum of $100.

Retired and disabled taxpayers also benefit from changes in the Maryland income tax law. The maximum retirement-income exclusion has been increased to $6,400. The exclusion is available to individuals 65 or older, or who are totally disabled.

Retired and disabled persons also may be entitled to additional exemptions. Taxpayers are entitled to a second $800 personal exemption if they are 65 or older, and there is another exemption for the blind.

Another change benefits artists. Those who earn at least half their income from the sale of works of art now may deduct the fair-market value of any works donated to a Maryland museum during the 1980 tax year.

To help taxpayers understand the changes in the law, free assistance with tax returns will be available on holidays, some weekends and during special evening hours from now until April 15, filing deadline.

Maryland Income Tax Division offices in Wheaton, Suitland and Bladensburg, which are open weekdays from 8:30 a.m., until 4:30 p.m., also will be open Saturday, April 4, 9 a.m. to 1 p.m.; Monday, April 6, 4:30 to 7 p.m. (telephone assistance only); Saturday, April 11, 9 a.m. to 1 p.m.; Monday, April 13, 4:30 to 7 p.m. (telephone assistance only), and Wednesday, April 15, 8:30 a.m. to 9 p.m.

The locations of the tax offices: Bladensburg -- Parkway Building, Suite 415, 5801 Annapolis Rd. (277-1240); Suitland -- Penn Silver Building, Suite 214, 5408 Silver Hill Rd. (568-0222), and Wheaton -- Wheaton Plaza North Office Building, Suite LL6 (949-6030).