  Anisotropy in the arrival direction distribution of ultrahigh-energy cosmic
rays (UHECRs) produced by powerful sources is numerically evaluated. We show
that, taking account of the Galactic magnetic field, nondetection of
significant anisotropy at $\approx 10^{19}$ eV at present and in future
experiments imposes general upper limits on UHECR proton luminosity of steady
sources as a function of source redshifts. The upper limits constrain the
existence of typical steady sources in the local universe and limit the local
density of $10^{19}$ eV UHECR sources to be $\gtrsim 10^{-3}$ Mpc$^{-3},$
assuming average intergalactic magnetic fields less than $10^{-9}$ G. This
isotropy, which is stronger than measured at the highest energies, may indicate
the transient generation of UHECRs. Our anisotropy calculations are applied for
extreme high-frequency-peaked BL Lac objects 1ES 0229+200, 1ES 1101-232, and
1ES 0347-121, to test the UHECR-induced cascade model, in which beamed UHECR
protons generate TeV radiation in transit from sources. While the
magnetic-field structure surrounding the sources affects the required absolute
cosmic-ray luminosity of the blazars, the magnetic-field structure surrounding
the Milky Way directly affects the observed anisotropy. If both of the magnetic
fields are weak enough, significant UHECR anisotropy from these blazars should
be detectable by the Pierre Auger Observatory unless the maximum energy of
UHECR protons is well below $10^{19}$ eV. Furthermore, if these are the sources
of UHECRs above $10^{19}$ eV, a local magnetic structure surrounding the Milky
Way is needed to explain the observed isotropy at $\sim 10^{19}$ eV, which may
be incompatible with large magnetic structures around all galaxies for the
UHECR-induced cascade model to work with reasonable jet powers.
