SMA PLT HAS NMAC WITH HELI IN TFC PATTERN.

Narrative

I WAS LEVEL AT 2300 FT. APPROX 5 MI ENE OF ST PETE WHEN I CONTACTED THE TWR. ST PETE TWR INSTRUCTED ME TO ENTER A R DOWNWIND FOR RWY 35R. THE TWR INFORMED ME THAT THERE WAS A COAST GUARD HELI DEPARTING RWY 4. WHEN I CONFIRMED SIGHT OF THE TFC; THE TWR INFORMED ME THAT THE TFC WOULD REMAIN E OF THE RWY AND CLRED ME TO LAND. I WATCHED THE COAST GUARD HELI PROCEED ON THE UPWIND PATH FOR RWY 4 AND I ENTERED THE R DOWNWIND FOR THE RWY 35R. AFTER WATCHING THE COAST GUARD TFC FOR A FEW SECONDS; I SAW HIM SUDDENLY REVERSE DIRECTION; AND IN A MATTER OF A FEW SECONDS MORE; CROSS IN FRONT OF MY ACFT AND ABOVE ME; MISSING ME BY APPROX 300 FT VERTICALLY AND 300 TO 400 FT HORIZLY. WITH VIRTUALLY NO TIME TO REACT; I MANAGED TO DSND SLIGHTLY AND TURN TO THE L SO AS TO PASS FARTHER BEHIND THE HELI AND FARTHER BELOW HIM. I EXPECTED THERE TO BE SEVERE DOWNWASH FROM THE HELI; BUT THERE WAS NONE. IT IS MY OPINION THAT THE HELI SUDDENLY REVERSED HIS DIRECTION OF TRAVEL OR AT LEAST EXTREMELY SHORTENED HIS PATTERN AND IGNORED TWR INSTRUCTIONS TO REMAIN E OF THE RWY. ALSO; ST PETE TWR SHOULD NOT HAVE CLRED ME TO ENTER THE ATA OR SHOULD NOT HAVE ALLOWED THE COAST GUARD TO REMAIN E OF THE RWY. TO ME; IT WOULD HAVE BEEN MUCH EASIER TO HAVE HAD THE HELI EXTEND HIS UPWIND FOR SPACING. AT THE TIME OF THE NEAR MISS; I WAS AT OR NEAR PATTERN ALT AND APPROX MIDFIELD ON THE DOWNWIND.