Using 13.53/fb of CLEO data, we have measured the ratios of the branching fractions R+(e) = BF(D+ --> K*0bar e+ nu_e) / BF(D+ --> K- pi+ pi+), R+(mu) = BF(D+ --> K*0bar mu+ nu_mu) / BF(D+ --> K- pi+ pi+) and the combined branching fraction ratio R+(l) = BF(D+ --> K*0bar l+ nu_l) / BF(D+ --> K- pi+ pi+). We find R+(e) = 0.74 +- 0.04 +- 0.05, R+(mu) = 0.72 +- 0.10 +- 0.06 and R+(l) = 0.74 +- 0.04 +- 0.05, where the first and second errors are statistical and systematic respectively. The known branching fraction BF(D+ --> K- pi+ pi+) leads to: BF(D+ --> K*0bar e+ nu_e) = (6.7 +- 0.4 +- 0.5 +- 0.4)%, BF(D+ --> K*0bar mu+ u_mu) = (6.5 +- 0.9 +- 0.5 +- 0.4)% and BF(D+ --> K*0bar l+ nu_l) = (6.7 +- 0.4 +- 0.5 +- 0.4)%, where the third error is due to the uncertainty in BF(D+ --> K- pi+ pi+).
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