HSI DISPLAY SWITCHED TO WRONG INPUT. EXP NAV VERSUS (THE CORRECT) EXP VOR ILS. CONSEQUENTLY; THE PF; FO; WAS FOLLOWING THE WRONG NAV INFO ON DEP FROM DCA AND THE ACFT PROBABLY PENETRATED P56. CTLR INTERVENED TO CORRECT THEIR FLT PATH AND PLTS THEN SAW THE DISCREPANCY.

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DELAYED DEP OUT OF DCA TO CLE ON OUR B737-500 GLASS COCKPIT DUE TO HVY TSTMS PASSING OVER THE ARPT. INITIAL FLT PLAN ROUTING WAS OFF OF DCA RWY 36 DIRECT TO JERES INTXN WHICH WAS 348 DEGS OUT OF DCA. HOWEVER; THE DCA DEP CALLS FOR INTERCEPTING THE 328 DEG RADIAL OUT OF DCA TO AVOID P56 JUST N OF THE ARPT. DURING TAXI OUT WE WERE CONSTANTLY USING THE RADAR AND DISTANCE DISPLAY CTLS TO CHK THE PROGRESS OF THE OVERHEAD TSTMS. DURING THIS EXERCISE; THE COPLT'S HSI DISPLAY CTL SOMEHOW GOT SWITCHED TO EXP NAV DISPLAY; AS IT SITS RIGHT NEXT TO THE DISTANCE DISPLAY CTLS. AFTER A NORMAL TKOF; I TOLD THE COPLT TO TURN L TO FOLLOW THE RIVER AND HE ASKED FOR HDG SELECT TO THAT DIRECTION. HE THEN ASKED FOR VOR/LOC ARMED; WHICH I DID. THE VOR CAPTURED ALMOST IMMEDIATELY AND HE TRACKED OUT PERFECTLY ON COURSE. UNFORTUNATELY; IT WAS THE RNAV COURSE 348 DEG RADIAL TO JERES INSTEAD OF THE 328 DEG RADIAL THAT WE HAD SET IN THE WINDOW BECAUSE HIS SELECTOR WAS MISTAKENLY SET TO EXP-NAV INSTEAD OF EXP VOR/ILS. OUR VERY LIGHT TKOF WT MADE FOR A STEEP CLB ANGLE AT FULL PWR (APPROX 23 DEGS NOSE UP) THUS MAKING THE RIVER DIFFICULT TO SEE. AT THIS TIME I WAS ALSO BUSY SWITCHING TO DEP AND MONITORING THE WX DISPLAY. SHORTLY THEREAFTER; I NOTICED THE RIVER DOWN LOW OUT OF THE L SIDE VIEW WINDOW. AT THIS SAME INSTANT; DEP CTL ASKED US TO TURN L TO INTERCEPT THE 328 DEG RADIAL. I ASKED THE COPLT TO TURN L TO INTERCEPT THE 328 DEG RADIAL; WHICH HE DID. HE STATED THAT HE HAD SHOWN BEING R ON COURSE AND WE SOON FOUND WHY. OUR MIS-SELECTED SWITCH GAVE US COURSE GUIDANCE ON THE 348 DEG RNAV COURSE INSTEAD OF THE 328 DEG VOR COURSE; RESULTING IN A POSSIBLE ENCROACHMENT INTO P56 AROUND THE LINCOLN MEMORIAL. SOMETIMES THE ABUNDANCE OF INFO ON THE FMS-GLASS COCKPIT EQUIP ACFT CAN BE DIFFICULT TO SORT OUT AND KEEP STRAIGHT.