We present below a study of the soft X-ray emission (0.1-2.4 keV) of the quasar 3C 273 with the Position Sensitive Proportional Counter (PSPC) instrument on the ROSAT satellite. The overall count rate shows variations of ~20 per cent in ~2d, a considerably higher degree of short-term X-ray variability than had been expected from previous studies. The count rates, when split into hard (1.5-2.4 keV) and soft (0.1-0.3 keV) energy bands, are not correlated, showing that two physically distinct emission components are present. The spectra are modelled best by a combination of two power laws with absorption at the galactic value. The photon number spectral index, Gamma_hard, of the harder power law is fixed at 1.5, the value determined by observations in the 2-10 keV band. The spectral index of the softer power law, Gamma_soft, is then determined to be ~2.7. There are small but significant variations in Gamma_soft which are not correlated with the soft count rate. We discuss the nature of this variable soft component in the light of present theories.