  We present ROSAT PSPC observations of the twin-jet radio galaxy 3C449. The
soft X-ray emission from this object is dominated by an extended halo with a
scale comparable to that of the radio source. The asymmetry of the X-ray
emission is reflected in that of the radio lobes, providing evidence that the
behaviour of the jets is strongly influenced by the external medium. A region
of reduced X-ray surface brightness coincident with the southern radio lobe of
3C449 suggests that the radio source has displaced thermal plasma from the
X-ray-emitting halo. However, the minimum pressure in the radio lobe is
considerably lower than our estimates of the pressure in the external medium.
We discuss the implications for the dynamics of the radio source.
