Starting from 12V, no more than two. If Vf=4, two LEDs drop 8V, leaving 4V across the current limiting resistor. At 700mA, the power dissipated in the resistor is 0.7*4 = 2.8W, so you will need a 5W resistor. The resistance is R=E/I = 4/0.7 = 5.7 Ohms. 5.6 Ohms is a standard value.
To run all four in series, you would need 16V plus the voltage across the current limiting resistor, say another 4V, for a total of 20V. You would use the same 5.6 Ohm 5W resistor...