keeping bitrate during conversion

hi,

I am trying to convert .mp4 videos to .3gp, it works, but there is a big 
difference in bitrate between the original and the converted copy:

ffmpeg -i media/470222.mp4 test3.3gp
ffmpeg version 0.4.9-pre1, build 4718, Copyright (c) 2000-2004 Fabrice 
Bellard
  built on Feb 28 2005 14:45:40, gcc: 3.2.3 20030502 (Red Hat Linux 
3.2.3-49)
Input #0, mov,mp4,m4a,3gp, from 'media/470222.mp4':
  Duration: 00:00:30.0, bitrate: 80 kb/s
  Stream #0.0: Video: mpeg4, 176x144, 12.00 fps
  Stream #0.1: Audio: amr_nb, 8000 Hz, mono
Output #0, 3gp, to 'test3.3gp':
  Stream #0.0: Video: h263, 176x144, 12.00 fps, q=2-31, 200 kb/s
  Stream #0.1: Audio: amr_nb, 8000 Hz, mono, 64 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press [q] to stop encoding
[h263 @ 0x443014]warning, cliping 1 dct coefficents to -127..127
...<snip/>...
[h263 @ 0x443014]warning, cliping 1 dct coefficents to -127..127
frame=  360 q=2.0 Lsize=     846kB time=30.0 bitrate= 231.0kbits/s
video:789kB audio:47kB global headers:0kB muxing overhead 1.184066%

of course I can set the bitrate parameters manually:

ffmpeg -i media/470222.mp4 -b 50 -ab 10 test4.3gp
ffmpeg version 0.4.9-pre1, build 4718, Copyright (c) 2000-2004 Fabrice 
Bellard
  built on Feb 28 2005 14:45:40, gcc: 3.2.3 20030502 (Red Hat Linux 
3.2.3-49)
Input #0, mov,mp4,m4a,3gp, from 'media/470222.mp4':
  Duration: 00:00:30.0, bitrate: 80 kb/s
  Stream #0.0: Video: mpeg4, 176x144, 12.00 fps
  Stream #0.1: Audio: amr_nb, 8000 Hz, mono
Output #0, 3gp, to 'test4.3gp':
  Stream #0.0: Video: h263, 176x144, 12.00 fps, q=2-31, 50 kb/s
  Stream #0.1: Audio: amr_nb, 8000 Hz, mono, 10 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press [q] to stop encoding
[h263 @ 0x351014]warning, cliping 1 dct coefficents to -127..127
[h263 @ 0x351014]warning, cliping 1 dct coefficents to -127..127
frame=  360 q=4.4 Lsize=     324kB time=30.0 bitrate=  88.6kbits/s
video:275kB audio:40kB global headers:0kB muxing overhead 3.161163%

question 1: is there a way to tell ffmpeg to keep the (overall) bitrate 
from the original?
question 2: is there a command which returns the bitrate(s) for a 
specific file?

thx

Phil