If you are the THE Homer Simpson you've got no chance!!! However, to lose the fat you will need to do the running or similar exercise. You can do hundreds of sit-ups a day and have that washboard stomach but you won't see it for fat unless your doing other 'fat burning' exercises as well.
Jogging will reduce your fat levels therefore reducing the size of your stomach while sit ups will tone your muscles producing more definition so the answer is a combination of both and properly performed "manual" sit ups are much better