Voters in the District of Columbia and Maryland will cast ballots today in primary elections for city, county, state and congressional offices. The winners will be party nominees for the general election on Nov. 2.

D.C. voters also will decide on an initiative requiring mandatory minimum sentencing for certain violent or drug-related crimes, and Marylanders will choose nonpartisan candidates for the school board.

In the District of Columbia, there will be party primaries for mayor, City Council chairman, council seats in Wards 1, 3, 5 and 6, two at-large council seats, and for the office of nonvoting delegate to Congress.

Only voters registered as Democrats, Republicans or D.C. Statehood Party members will be allowed to vote in the primaries for those offices. However, all registered voters, including independents, will be able to vote on the mandatory minimum sentencing initiative, called Initiative No. 9.

In Maryland, there are Democratic and Republican primaries for governor and lieutenant governor, the U.S. Senate, Congress, the state legislature, county executive and County Council. Republicans also will choose a nominee for state comptroller.

In Prince George's and Montgomery counties, voters also must choose school board candidates. Winners of the school board races will face a runoff in November.

Prince George's residents also must vote on nominees for clerk of circuit court and sheriff. In Montgomery County, voters will choose judges for the 6th Judicial Circuit, clerk of circuit court, sheriff and state's attorney.

In Maryland, all registered voters can vote for school board candidates, but only registered Democrats or Republicans are eligible for the party primaries. Party members will find on their ballots names of candidates seeking seats on county Republican and Democratic central committees.

Maryland elections officials expect about 35 percent of the state's registered voters at the polls today, less than the 42.5 percent that voted in the 1978 primaries. There are fewer fiercely contested primaries this year, they said.

Polls in the District of Columbia, Prince George's and Montgomery counties will be open today from 7 a.m. to 8 p.m.

For additional information on voting in Washington call the Board of Elections and Ethics at 347-4509; in Prince George's call the Board of Elections at 952-3270; in Montgomery at 279-1507.