Amid the chilly drift of postwar German novels, this import is happily ingratiating and incongruously heartening, although events and situations reveal the all-too-familiar spectacle of individuals gnawing at the collective anxiety of our times. The ""fortress"" of the title is an abandoned edifice, utilized by the Government to house war refugees, while new--and one would sense, chimerical--tantalizingly soon-to-be available apartments are promised. Yet to Hugo, seedy, titular head of a family--an untidy cluster of illusions, abortive plans, and petulant tantrums--the fortress becomes, somehow, a home bulwark against the State. For Hugo this is a wavering, unfocussed campaign, which has as its climax a wild and wet defiance against the fire hose might of Authority. But this is Hugo's battle, for his family is crumbling away--a wan wife, a religious buff; a senile mother who can spit with true aim; contemptuous older sons away from home; Albert, sent to a reform school for ""anti-social"" behavior; Mimo who turns to prostitution; little Bruno, the blessing. But through murder, the deceptions of children, the certainty of futile tomorrows, Hugo has, nonetheless, a winning stubborn individuality, an urge to place thumb to nose. Beautifully translated, though a bit crowded, this novel has both irreverence and compassion.