We report a measurement of the fraction of dijet events with a
rapidity gap between jets produced by color-singlet exchange in pbar p
collisions at sqrt s = 630 GeV at the Fermilab Tevatron.  In events with two
jets of transverse energy E^jet_T > 8 GeV, pseudorapidity in the range 1.8 <
|eta^jet| < 3.5 and eta_1, eta_2 < 0, the color-singlet exchange fraction is
found to be R = [2.7 +/- 0.7(stat) +/- 0.6(syst)]%.  Comparisons are made with
results obtained at sqrt s = 1800 GeV and with theoretical expectations.