  Using first-principles calculations, we show that the (001) surface of the
ferromagnet La$_{1-x}$Sr$_{x}$MnO$_{3}$ under epitaxial compression favors
antiferromagnetic ordering in the first few surface layers, coexisting with
ferromagnetic bulk order. The change in magnetic order is accompanied by a
marked surface-related spectral pseudogap, signaling a metal-insulator
near-transition at the surface. All surfaces exhibit huge outward relaxations
an rumpling of the MnO$_{2}$ and LaO surface planes, causing a distinct shift
in work function. The AF phase is an extreme surface-assisted case of the
combination of in-plane AF super-exchange and vertical FM double-exchange
couplings that rules magnetism in manganites under in-plane compression.
