We present echelle spectroscopy in the 3500 to 10300 Angstroms range for two positions of the galactic H ii region M17. The data have been obtained using the 2.1 m telescope at Observatorio Astronomico Nacional in San Pedro Martir, Baja California. We measure the intensities of 160 emission lines, in particular 36 permitted lines of C(+) , N(0) , N(+) , N(++) , O(0) , O(+) , Ne(0) , Si(0) , and Si(+) . We determine electron temperatures and densities using different line intensity ratios as well as abundances from collisionally excited lines for a large number of ions and elements. We derive the He(+) , C(++) and O(++) ionic abundances from recombination lines, these nebular values are almost independent of the temperature structure of the nebula. We determine accurate t(2) values by comparing the O(++) ionic abundance obtained from collisionally excited lines and recombination lines. A comparison of the chemical abundances of the Sun, M17, M8, and the Orion nebula is made. We present strong observational constraints based on abundance ratios and compare them with recent models of galactic chemical evolution.