Virginia Del. Robert E. Harris (r-Fairfax) announced yesterday that he will run for Congress in Northern Virginia's 8th congressional district, a seat now held by another Harris, two-term Democrat Herbert E. Harris II.

Del. Harris joins Fairfax County Board of Supervisors Chairman John F. Herrity in a race for the Republican nomination that will be decided in a June 13 primary.

Del. Harris, who in past elections has been confused with Rep. Harris, said at a press conference yesterday that for "uninformed voters there is probably a 10 percent confusion band" between hinself and ReP! Harris. He added, however, that the "hard-core Republican base knows who I am and who He (Rep. Harris) is."

A third-term delegate, Harris, 43, said the national economy faces "an uncertain future" because of "the same old Democratic approach to government which is more spending and taxing, more deficits, more anti-business attitude."

Harris, who is employed by Rockwell International as division director of energy and environmental affairs, said he advocates less government in state and local affairs and "greater emphasis on the right of individual self-determination."

Harris declined to talk about his earlier statements about the health of Republican opponent Herrity. Last month, referring to Herrity's two heart attacks in 1976. Harris questioned whether Herrity could stand the stress of a campaign. "I have no further comment regarding Mr. Herrity's health." Harris said yesterday. "I consider that an issue that is closed.

Harris was one of two Northern Virginia delegates to vote against a bill rejected last week by the House calling for a one-cent sales tax increase to help Metro subway expenses. He said he voted against the bill because of his 'no sales tax increase" campaign promises last year.

Del. Robert L. Thoburn (R-Fairfax) said yesterday he plans to announce his candidacy for the 8th district seat the first week of April.