Five Northern Virginians this week added their names to the swelling ranks of candidates seeking seats in the Virginia House of Delegates.

In Fairfax County -- split into four House districts with three seats each in the recent redistricting -- three residents announced their candidacies. Democrats Michael J. Hershman and Republican Robert C. Brostrom said they plan to run for a seat in the new 51st District, covering southwestern Fairfax County. In the 52nd District, including the county's southeastern corner, Republican Nelson P. Jackson added his name to the long list of candidates.

In Alexandria, Marian Van Landingham became the second Democrat to announce her candidacy in the two-seat 22nd District.

In Arlington, incumbent James F. Almand, a Democrat, is making a bid in the new three-member 22nd District. Fairfax County

In the 51st District, Brostrom is making his first bid for public office. Brostrom, an employe of the C & P Telephone Co, has been active in Republican politics and is currently serving as secretary of the party's Fairfax organization. He said he is a strong supporter of President Reagan's economic program and would like to see the same attitude taken toward state tax cuts: in particular, a repeal of the state's food tax. Brostrom said he supports equal rights not vote for ratification of the ERA. He does not support extension of the Voting Rights Act.

On the Democratic side, Hershman is one of three Democrats seeking nomination from the 51st District. Hershman has served as a staff member on the Senate Watergate committee and is a past deputy auditor general of the General of International Development. He is making his first bid for elective office. Currently, Hershman is an executive with a private firm investigating white collar crime. He said the state needs to revise its criminal code to make it harder for frequent offenders to be paroled. In addition, he said, instead of spending more money on criminals, the state should begin to funnel more funds into programs for the victims of crimes.

Hershman, president of the Fairfax County Victims Assistance Network supports ratification of the ERA.

Jackson, a Republican seeking a seat in the 52nd District, is a retired naval officer who is currently an executive with the American Defense Preparedness Association. He said he supports mandatory sentencing for some crimes and would like to see more state concern for crime victims. A self-described fiscal conservative, Jackson said the state needs to reform its regulatory policies. In particular, he said, the state needs to streamline its educational policies and send more administrators back to the classroom. He supports an increase in teacher salaries. Alexandria

Van Landingham is running for a seat in the new two-member 21st District. It is her second bid for elective office. In 1979, she ran unsuccessfully for the Alexandria City Council. Van Landingham supports legislation to preserve and encourage the construction of rental housing in Alexandria. A long-time civic activist, she was past president of the Torpedo Factory Artists Association and serves on the board of the Alexandria Volunteer Bureau. Van Landingham supports ratification of the ERA. Arlington

Almand is seeking a third term in the House of Delegates. An advocate of tenant rights, Almand sponsored a number of housing bills this year aimed at protecting tenants facing condominium conversions. He said he would continue to fight for the preservation of moderate-cost rental units.

Almand, a member of the House Courts of Justice Committee, also notes that he supported ratification of the Equal Rights Amendment.

Party primaries have been set for Sept. 8; the general election will be Nov. 3.