There's no way to answer your question correctly. What laptop are you looking at? What desktop are you looking at? How expensive is electricity in your region? How long do you plan to use the laptop?
I'm going to go and make a lot of assumptions and say no. For example my laptop with 17" screen has 90 W power supply. On the other hand, PCs usually use less than 200 W. The fact that there's a 400 W power supply means that it can provide up to 400 W for internal components at peak power consumption. It doesn't mean that the computer is using 400 W all the time. Also, 200 W for a monitor is really a lot, unless you compare laptop LCDs with CRTs.
Laptops are more expensive and their maintenance is more expansive and I do not believe that during its lifetime a laptop will be able to pay for itself.