starter help

[hangbelly]

My 1990 200 merc is getting progressivly harder to start. she turns over fine when I turn the key but the starter disingages after a second or two. I am turning the key and holding on start but she wont keep crankin, just a short crank then it just quits turning over like I turned off the key. I have to turn the key again to crank it again. I get one short crank every time I turn the key. It turrns strong and fast, just short. (not a weak battery problem) Its been doing it for awhile now and always starts but the cranks are getting shorter and I have to try it 5 or 6 times to get it going even when warm. Starter? solinoid? ignition? Any one have a similar problem they have delt with?