I have the answer from the distributor. They say, that the sensor installed in the DS-2CD2032-I 3 megapixel camera is the Aptina AR0330 2304x1536, 1/3", 5.07mm(H)x3.38mm(V).
The 3Mpix 4:3 stream uses physical 2048x1536 pixels (2048 out of 2304 horizontal).
The 2Mpix 16:9 uses physical 2304x1296 (scaled 20% down to 1920x1080).
So according to the official info it is the 3,5 Mpix camera.
I think, I have to find this lost-somewhere-test-chart and try to verify this, although the results may be not clear - the camera has very simple, small lens and this affects high resolutions in siginificant way.