Infrared laser-microwave double resonance spectroscopy is used to observe the Stark effect of tunneling transitions within the nu(1) and nu(3) hydrogen stretching states of NH3. Dipole moments for 11 J,K states of nu(1) and 3 J,K states of nu(3) are measured to high accuracy. These data, combined with previous measurements in the ground and excited bending states, give a dipole moment function (in Debye) of : mu(nu 1 nu 2 nu 3 nu 4)=1.5610+7.2x10(-3)(nu(1)+1/2)-2.271x10(-1)(nu(2)+1/2)+3.75x10(-2)(nu(3)+1)-1.65x10(-2)(nu(4)+1)mu(e)=1.561 D is the first experimental measurement of the NH3 equilibrium moment. These results are also used to analyze and recalculate the dipole moment measured by Shimizu and co-workers in a nu(NH)=5 excited state of NH3.