The stability of finite gaseous disks against large-scale perturbations under the influence of spherical, massive haloes have been studied. A surface-density distribution consistent with the observed spiral-tracer profiles in disk galaxies is considered for the disk. It is found that growing eigenmodes with both 'trailing' and 'leading' spirals exist in 'cold' disks for a wide range of values of the halo mass and its radius. The amplification rates of the unstable modes reduce as the ratio of the mass of the halo to the mass of the disk is increased. A uniform halo is not very effective towards stabilizing the disk against these modes. The results from the present study are considered vis-a-vis previous studies on the global modes of self-gravitating disks.