  We estimate the decay constants $f_\pi$ and $f_K$ of the light mesons within
a relativistic quantum-field model of interacting quarks and gluons confined
analytically. The necessary physical parameters, the quark masses $m_u$ and
$m_s$, the coupling constant $\alpha_s$ and the confinement scale $\Lambda$
have been obtained from our previous investigation on the meson ground states,
orbital and radial excitations by using the ladder Bethe-Salpeter equation. Our
approach provides a solid framework to compute the meson spectra, the lowest
glueball state and decay constants of pseudoscalar mesons (as well as other
physical observables) nonperturbatively from the basic principles of QCD and
QFT.
