WAKE ENCOUNTER.

Narrative

MY ACFT WAS A PA28-181. WHEN I OBTAINED VISUAL CONTACT WITH DCA I CALLED ATC WITH A RPT OF THE ARPT IN SIGHT. THE CTLR DID NOT CLR ME FOR THE VISUAL TO EITHER RWY 33 OR RWY 36; BUT RESPONDED THAT I COULD EXPECT THE ILS 36. I ELECTED TO REMAIN IFR; PRIMARILY FOR WAKE AVOIDANCE. I WAS PLACED ON ABOUT A 3 MI R DOWNWIND FOR THE ILS; AND WHEN SE OF THE FIELD; DSNDED TO 1800 FT. ACR TFC APPEARED TO BE APCHING IN A STEADY STREAM FROM THE S; ESSENTIALLY TRACKING THE LOC NBOUND AND DSNDING AT WHAT APPEARED TO BE A FAIRLY STEEP ANGLE (MORE THAN 3 DEGS) TO INTERCEPT THE GS ABOUT 1 MI S OF THE OM (OXONN). AFTER PASSING ABEAM OXONN AND FLYING PERHAPS 3 MI MORE; I WAS TURNED BASE; AND THEN FINAL. AS I WAS BEING TURNED FOR THE INTERCEPT; ATC ADVISED THAT I WAS INTRAIL OF A 757; THAT I WAS CLRED FOR THE ILS 36 AND 'CAUTION WAKE TURB.' AT THAT POINT; THE 757 HAD STEEPLY DSNDED FROM WELL ABOVE 1800 FT THROUGH THAT ALT JUST PRIOR TO REACHING THE MARKER; I.E.; MY TRACKING OF THE LOC AT 1800 FT TO GS INTERCEPT WOULD PLACE ME BELOW AND CONVERGING UPON THE 757'S-FLT PATH. I DO NOT KNOW IF THE 757 WAS FLYING THE ILS OR ON A VISUAL APCH. I WOULD ESTIMATE THAT WHEN I INTERCEPTED THE LOC THE 757 WAS AHEAD OF ME BY ABOUT 3-4 MI. AS I WAS ABOUT 1 MI S OF OXONN; THE 757 WAS OUTSIDE THE MM AND I ENCOUNTERED WHAT I BELIEVE TO HAVE BEEN A MILD FORM OF WAKE TURB. IN WHAT HAD OTHERWISE BEEN SMOOTH AIR; THE TURB CONTAINED A STRONG ROLLING MOTION THAT REQUIRED ABOUT 3/4 AILERON DEFLECTION TO RETAIN A NEAR- LEVEL ATTITUDE. THAT TURB LASTED FOR ONLY A FEW SECONDS AND; ONCE I ESTABLISHED ON THE GS; I DID NOT AGAIN EXPERIENCE IT. SHORTLY THEREAFTER I CONTACTED DCA TWR; WHO RPTED THE 757 AT THE MM AND I WAS CLRED TO LAND. THE LNDG WAS WITHOUT INCIDENT. I WAS SURPRISED TO SEE THAT ATC WAS DSNDING THE AIRLINE TFC (AND; PARTICULARLY THE 757 I FOLLOWED) FROM WELL ABOVE THE GS; AND ALSO VECTORING LIGHT ACFT AT 1800 FT TO INTERCEPT THE LOC SEVERAL MI S OF THE MARKER. WHILE THERE MAY HAVE BEEN 'LEGAL' IFR SEPARATION BTWN THE 757 AND MY ACFT; THE WAKE TURB WAS UNMISTAKABLE AND I WOULD SUGGEST THAT THE SEPARATION BEHIND 757'S BE INCREASED TO TAKE INTO ACCOUNT WHAT I HAVE READ IS THEIR WAKES. IN ADDITION; IN THE FUTURE; I WILL BOTH NOT TRUST OPS UNDER IFR; AND FLYING THE GS; TO KEEP ME FREE FROM WAKE TURB ENCOUNTERS; AND REALIZE THAT AS PIC I SHOULD HAVE INFORMED ATC THAT THE INTRAIL SEPARATION; GIVEN THE DSNDING FLT PATH OF THE 757; WAS UNACCEPTABLE TO ME.