Combine first 4 ingredients in a colander lined with paper towels; let stand 20 minutes. Drain and squeeze excess moisture from potato mixture. Transfer potato mixture to large bowl; add onion, flour, and pepper. Toss well; stir in egg whites.
Heat 1 tablespoon oil in a large nonstick skillet over medium-high heat. Spoon 1/3 cup batter for each of 5 latkes into pan; cook 4 minutes on each side or until browned. Repeat procedure with 1 tablespoon oil and remaining batter.