Global electric properties, distributions of the induced electromagnetic fields, electron density, temperature, and plasma potential in the 500 kHz planar-coil inductively coupled plasma source have been investigated; The transitions between the two (E and H) discharge operating regimes with variation of input power and operating gas pressure have been demonstrated. It has been shown that the E<->H transitions are accompanied by the resonant minima in the rf power reflection coefficient, which are characteristic for mode jumps in electron cyclotron resonance and microwave slot-excited discharges. The optical emission spectra of argon atoms and ions together with global power balance arguments suggest that the step-wise ionization via the excited states of argon atoms and ions is presumably a mechanism which is responsible for hysteresis. The achieved high plasma density with a high homogeneity level, and low electron temperature and plasma potential imply that the studied plasma source is promising for industrial applications.