Rev. Al Sharpton to Gov. Chris Christie -- I Can Help You KEEP the Weight Off!

Al Sharpton wants to be the Mickey to Chris Christie's "Rocky Balboa" ... telling TMZ he'll personally train the Gov's obese ass to ENSURE he doesn't regain the weight he's lost after Lap-Band surgery.

Sharpton -- who's dropped a ton of weight WITHOUT the use of surgery -- was in NYC today when we asked if he feels voters will judge Christie negatively for using the Lap-Band shortcut, instead of dropping the poundage through diet and exercise.

Rev. Al essentially told us the ends justify the means ... and insists Christie needs to focus on maintaining the weight loss ... even offering to be Christie's "maintenance man."

But the weight loss doesn't guarantee votes, according to Rev. Al ... who pointed out, "I lost weight, I'm still not president."