PA28 PLT ENTERED DCA CLASS B AIRSPACE WITHOUT CLRNC.

Narrative

DEPARTED ANP ARPT VFR. 1 MI W OF ANP; CALLED WASHINGTON APCH ON 124.2. REQUESTED VFR FLT FOLLOWING DIRECT TO LEESBURG; VA (JYO) AT 4500 FT VFR. AFTER SQUAWK CODE WAS GIVEN; I WAS ASKED ALT. I SAID 1900 FT CLBING TO 4500 FT. ATC SAID 'NO CONTACT' YET BUT WOULD LET ME KNOW. ABOUT 2 MINS LATER; ATC ASKED IF I WAS FAMILIAR WITH THE AREA. I ANSWERED 'AFFIRMATIVE.' HE THEN TOLD ME I WAS RADAR CONTACT; SHOWING 3000 FT AND CLBING AND NOW 500 FT INTO THE CLASS B AIRSPACE. (CLASS B AIRSPACE BEGAN AT 2500 FT.) I APOLOGIZED AND HE CLRED ME INTO CLASS B AND DIRECTED ME TO CONTINUE CLB TO 4500 FT. HDOF TO IAD WAS UNEVENTFUL. THIS INCIDENT MAY NOT HAVE HAPPENED IF I HAD PAID CLOSER ATTN. I WAS SO 'USED' TO GETTING A SQUAWK CODE; AND TALKING TO ATC THAT I ASSUMED I WAS CLRED INTO CLASS B AIRSPACE EVEN WITHOUT THE CORRECT PHRASEOLOGY. ALSO; ATC NEVER SAID 'REMAIN CLR OF CLASS B' OR NEVER TOLD ME TO HOLD ALT WHEN I TOLD THEM I WAS CLBING AND PASSING 1900 FT FOR 4500 FT. BEFORE FREQ CHANGE; I APOLOGIZED AGAIN AND THE CTLR REPLIED WITH 'NO PROB; HAVE A GOOD FLT.'