We propose a novel adaptive scheme that operates in association with either of two admission control policies, the multiple guard channel (MGC) and the multiple fractional guard channel (MFGC) policies. We provide two different implementations of the scheme, which adapt the configuration parameters of the associated policy according to the perceived QoS. The numerical evaluation carried out shows that the QoS objective is met with an excellent precision and the convergence period is much shorter than in previous proposals (approximately in the range of a thousand seconds), confirming that our approach can satisfactorily deal with the nonstationarity of an operating network. Two other key features of our scheme are its simplicity and time independency.