Voters in six of Northern Virginia's new House of Delegates districts will go to the polls Tuesday to decide on five Republican and two Democratic primary contests.

The polls will be open from 6 a.m. to 7 p.m.

Five of the six districts with contests are in Fairfax County; the other is in Prince William County.

The primary contests are part of a special House of Delegates election being held this year in new House districts. The redistricting plan, ordered by the courts, carves the state into 100-single member districts.

Three incumbent Republicans face challenges from conservative opponents, and those races have attracted the most attention. Five-term Del. Robert E. Harris, for instance, is running hard against former delegate Robert L. Thoburn in the new 40th District, which includes Centreville, Fairfax Station, Greenbriar, Clifton and two precincts in western Prince William County. The winner of the primary will face Prince William Democrat Claude (Brad) Bradshaw in November.

Another incumbent Republican who calls himself a moderate-conservative, James H. Dillard II, faces a challenge from conservative Gordon S. Jones in the 41st District, which includes Burke, Newington and part of West Springfield in southern Fairfax. Dillard was first elected in 1971 but sat out two years when a challenge from the right unseated him in 1977. No Democratic candidate has filed in the 41st.

The third moderate Republican incumbent being challenged, former Fairfax City attorney John H. Rust Jr., is trying to head off Stephen E. Gordy, a retired Army colonel, in the 37th District, which includes Fairfax City and nine surrounding precincts. The winner of that contest will face the winner of the Democratic primary between James W. Benson and Fred J. Ricci, both running for office for the first time.

The other primaries do not involve incumbents, although several candidates are seeking a chance to compete in what will likely be spirited runs against incumbents in November. Two young Republicans, James N. Burroughs and David G. Sanders, are competing in the 35th District for a chance to challenge Democratic incumbent Dorothy S. McDiarmid, the senior member of the Northern Virginia House delegation. The 35th includes parts of Vienna and Falls Church.

Two Democrats who have run before, Wayne M. Lynch and Nora A. Squyres, are facing off in the inner-Fairfax 38th District between Rte. 50 and Little River Turnpike. The incumbent there, Republican Gwendalyn F. Cody, is a conservative who won her seat last year.

The final GOP contest takes place in the 51st District, a Prince William seat that includes Dale City and Lake Ridge. F. Clancy McQuigg and Smith William Young are seeking to oppose Democrat Del. David G. Brickley.