Primary elections will be held tomorrow in both the District of Columbia and Maryland. Polls will be open in both jurisdictions from 7 a.m. to 8 p.m.

Ballots will be cast in the District to nominate candidates for mayor, congressional delegate, City Council chairman, council member at large and council members from wards 1, 3, 5 and 6.

In the District, only persons registered in the Democratic, Republican, D.C. Statehood, Socialist Workers or U.S. Labor parties will be allowed to vote.

In Maryland, registered Democrats and Republicans throughout the state will choose party candidates for a range of posts, from governor and attorney general to congressional and state legislative seats and county offices.

Maryland voters no registered as Democrats or Republicans may vote only in school board races.

In the District, write-in votes will be permitted. No write-ins will be allowed in the Maryland primaries.

In Washington, residents precinct 123 who formerly voted the old Congress Heights Elementary School, now vote at the new one, at 6th Street and Alabama Avenue SE. Residents of precinct 24 who in the past have voted at the Morgan Elementary School will now vote at the Marie Reed Learning Center, 2200 Champlain St. NW.

Maryland residents wishing more information should call their county elections boards. In Montgomery, the number is 279-1507; in Prince George's 952-3270; in Howard County 997-7644.

In the District additional information may be obtained from the D.C. Board of Elections and Ethics, 347-9725, or the League of Woman Voters, 785-2616.