It is shown that pulsar radio emission can be generated effectively through a streaming motion in the polar-cap regions of a pulsar magnetosphere causing nonresonant growth of waves that can escape directly. As in other beam models, a relatively low-energy high-density beam is required. The instability generates quasitransverse waves in a beam mode at frequencies that can be well below the resonant frequency. As the waves propagate outward, growth continues until the height at which the wave frequency is equal to the resonant frequency. Beyond this point, the waves escape in a natural plasma mode (LO mode). This one-step mechanism is much more efficient than previously widely considered multistep mechanisms.