  We report on a deep search for radio pulsations toward five unidentified ASCA
X-ray sources coincident with EGRET gamma-ray sources. This search has led to
the discovery of a young and energetic pulsar using data obtained with the new
Wideband Arecibo Pulsar Processor. PSR J2021+3651 is likely associated with the
X-ray source AX J2021.1+3651, which in turn is likely associated with the COS B
high energy gamma-ray source 2CG 075+00, also known as GeV J2020+3658 or 3EG
J2021+3716. PSR J2021+3651 has a rotation period P = 104 ms and P_dot =
9.6x10^{-14}, implying a characteristic age ~17 kyr and a spin-down luminosity
E_dot ~ 3.4x10^{36}ergs/s. The dispersion measure DM ~ 371 pc cm^{-3} is by far
the highest of any observed pulsar in the Galactic longitude range 55 < l < 80.
This DM suggests a distance d > 10 kpc, and a high gamma-ray efficiency of
\~15%, but the true distance may be closer if there is a significant
contribution to the DM from excess gas in the Cygnus region. The implied
luminosity of the associated X-ray source suggests the X-ray emission is
dominated by a pulsar wind nebula unresolved by ASCA.
