Rep. D. French Slaughter, a conservative Republican from rural Culpeper, Va., announced yesterday that would run for a second term as a House member.

Slaughter, 60, said he would push for an amendment to return voluntary prayer to public schools, and for a health care savings program as an alternative to Medicare. He credited Reagan administration economic policies with lowering interest rates and inflation.

Slaughter is a member of the House committees on Science and Technology and Small Business. In his first term, Republican colleagues said he kept a low profile in Congress but has been visible in his 7th Congressional District, appearing often at local gatherings.

T. Dean Reed, 55, a former journalist and Washington business consultant, has indicated he might challenge Slaughter in the November election. But one of the best known Democrats in the area, Del. Alson H. Smith, announced this year that he would not run for the House despite proddings from Democratic officials who viewed Smith as their best chance of unseating Slaughter.

The 7th District is a largely rural district that stretches between Manassas and the West Virginia border, and runs as far north as Winchester and as far south as Richmond.

The district is one of the most conservative in Virginia, although it encompasses several moderate enclaves, such as Charlottesville and Fredericksburg. The Shenandoah Valley was the home of the Byrd family dynasty, and Slaughter was a former loyal lieutenant in the organization of Harry F. Byrd Sr. during the 20 years he served in the Virginia General Assembly.

His record as a supporter of segregated schools, the poll tax and sterilization of epileptics and retarded persons and his opposition to civil rights legislation were major issues during the campaign two years ago, which was one of the most expensive campaigns ever waged in that district. But Slaughter won with 56 percent of the vote.