If you don't want any embedded end-of-line characters, then the @"..." syntax won't help.
But, you can use the concatenation operator (+):
const string format = "{0,3} | {1,6} |A {2,6} |B {3,4} |C {4,4} |D {5,4} |E {6,4}" +
" |F {7,4} |G {8,3} |H {9,4} |I {10,4} |J {11,3} |K {12,2}" +
" |L {13,2} |M {14,6} |N {15,6} |O {16,6} |P {17,6} |Q {18,1}" +
" |R {19,4} |S {20,2} |T {21,4} |U {22,4} |V {23,3} |W {24,8}";