  This paper investigates higher order wave-type equations of the form
$\partial_{tt}u+P(D_{x})u=0$, where the symbol $P(\xi)$ is a real,
non-degenerate elliptic polynomial of the order $m\ge4$ on ${\bf R}^n$. Using
methods from harmonic analysis, we first establish global pointwise time-space
estimates for a class of oscillatory integrals that appear as the fundamental
solutions to the Cauchy problem of such wave equations. These estimates are
then used to establish (pointwise-in-time) $L^p-L^q$ estimates on the wave
solution in terms of the initial conditions.
