Spectra of weakly bound hydrogen-argon complexes have been studied at high spectral resolution (0.04-0.10 cm(-1)) using a long-path (154 m), low-temperature (77 K) absorption cell and a Fourier transform infrared spectrometer. The observations cover a wide spectral range from the far-infrared D-2-Ar S-0(0) band at 180 cm(-1) to the near-infrared H-2-Ar S-2(1) band at 8600 cm(-1). Compared to earlier studies, the new results have considerably improved resolution and accuracy. They also extend to new regions, namely the first overtone band of H-2 and the pure rotational band of H-2 and D-2, and they include weak transitions involving excitation of the van der Waals stretching motion. These data serve as a basis for determining a greatly improved three-dimensional intermolecular potential energy surface for the hydrogen-argon system in the following paper.