The first debate between the Republican and Democratic candidates for Congress in Northern Virginia's 8th District last night was marked by accusations from the GOP challenger while the Democratic incumbent stood on his own record.

John F. (Jack) Herrity, the Republican candidate and chairman of the Fairfax County Board of Supervisors, opened the debate by accusing his Democratic opponent of advocating "waste and excessive government spending."

Rep. Herbert E. Harris II, a two-term incumbent in the 8th District, at first chose not to respond to Herrity's attacks, opting instead to say that he has been an effective leader in responding to the needs of Northern Virginia, for instance by supporting the Metro system.

The debate, filmed last night at WJLA-TV. Channel 7, for broadcast at 7 p.m. Sunday and 6:30 a.m. Tuesday, brought out sharp differences between the candidates and set the stage for what is expected to be a close and bitter race between two men who frequently insulted each other when thy served together in the early '70s on the Fairfax County Board of Supervisors.

Throughout the questioning by Channel 7's Gary Axelson. Herrity tried to paint Harris as a big spender who gives lip service to the need to control inflation but votes for inflationary programs.

Harris, refraining for the most part from direct replies to Herrity, said he favors 80 percent federal support of the 100-mile Metro system. He said that as a member of the House District of Columbia Committee he is in a good position to get the federal funding.

Herrity said he has checked with the Republican leadership in the House and been told he would get a seat on the Public Works and Transportation Committee. From that position, Herrity said he would be in a powerful position to get federal money for Metro.

In his one sharp rejoinder to Herrity, Harris said he "hated to embarrass his opponent" but it is the District of Columbia committee that funds Metro.

Also participating in last night's debate was independent candidate Charles E. Coe, 39, who said he was a moderate and that he represented the "average guy" who wanted his taxes cut.

On issues of national health insurance, the Equal Rights Amendment and collective bargaining for public employes Harris and Herrity were on opposite sides. Harris said he supports the ideas and Herrity said he opposed them.