How to reduce resistor power consumption?
If the LED Vf is 2 V, and the source is 10 V, then between whatever resistors you use and the uppermost transistor, they will consume 4x as much power as the LED does.

As a trivial solution to the problem as you have stated it, if you take your current design and split each 20-ohm resistor into two 10-ohm resistors in series, then you will have less than 3 W consumed by each resistor.

Reducing the source voltage will reduce the overall power consumption of the circuit, and improve the efficiency, but might require re-adjusting your resistor values to keep the LED power as high as you want it.

But really this is a horrifically inefficient way to power a 3 W LED. For a real-world design you should consider using a constant-current circuit based on switching power supply concepts. Or at least use a larger number (3 or 4) of smaller LEDs in series to improve the efficiency.