GCM-dependent, radiatively constrained cloud amount fields could be preferrable to currently available observed fields for calculating radiative fluxes in GCM's used in long-range weather forecast studies. Motivated by this premise, we formulate an economical effective cloud algorithm for GCM's called ''SATCLD,'' which utilizes compact, readily accessible analyses of observed satellite-derived radiative flux data. We then examine the plausibility of preliminary effective cloud fields. Analysis of SATCLD and other cloud fields and associated radiative fluxes (diagnosed by our GCM's cloud radiation model from observed atmospheric temperature and water vapor data) also provides some insight into biases in our GCM's cloud radiation model and surface albedo field. ''SATCLD'' generates effective low and high cloud amounts at each GCM grid point by minimizing the sum of the squares of the local residual (i.e., model-diagnosed minus observed) shortwave and longwave radiative fluxes. The preliminary SATCLD effective cloud amount fields seem plausible in many respects, based upon comparison with the satellite-derived 3DNEPH and surface-based SFCOBS analyses. In the tropics the SATCLD effective high cloud amount is rather well correlated with 3DNEPH, while systematic differences in low cloud amount are evident in July. Off the west coasts of Central and South America and southern Africa, the SATCLD effective low cloud resembles SFCOBS in July. At mid-latitudes the strongest similarities are between SATCLD versus 3DNEPH high cloud amount in July and SATCLD versus SFCOBS low cloud amount over the oceans. The SATCLD analysis is ill conditioned in the polar night region. Limitations of the present scheme as well as deficiencies in our GCM's cloud-radiation model and surface albedo fields and in the archived satellite data are discussed. Suggestions are made for reducing discrepancies between effective versus real clouds without sacrificing consistency between GCM-diagnosed versus observed radiative fluxes.