Drastic changes of 0g+'0g+ (p,t) analyzing powers for the isotopes Zr, Mo, Ru, and Pd are explained in terms of interference between one-step and (p,d)(d,t) sequential transfer amplitudes of comparable magnitudes. Dependence of the analyzing powers on reaction Q values, incident energies, and nuclear structures is interpreted from the interference. Analyzing powers for (t,p) reactions can be understood similarly. A test of time reversal invariance in nuclear reactions with use of the analyzing powers for (p,t) and (t,p) reactions is discussed. NUCLEAR REACTIONS Vector analyzing power Ay() for g.s. (p,t) on Zr92, Mo94,96,98, Ru100,102,104, Pd104,106,108,110, Ba138, Ep=22 MeV, first- and second-order DWBA. Comparison with (t',p).