Best Buy has embarked on an aggressive campaign to dominate the HDTV market with the first shipments of the Panasonic 56-inch rear-screen projection HDTVs to 135 of its stores in 16 cities, along with RCA and Sony models. The sets will be used to display high-definition broadcasts and other programming. The mass merchant plans to have HDTVs on display in all of its 312 stores by April 1999.