The Sr-induced ordered superstructures on the Si(100)-2x1 surface have been studied using ultrahigh vacuum scanning tunneling microscopy and low-energy electron diffraction (LEED) fur metal coverages (theta) below one monolayer (ML). At very low coverages (theta less than or equal to 0.01 ML) Sr atoms adsorb as isolated atoms or small clusters, At submonolayer coverages of similar to theta greater than or equal to 0.12 ML we have observed the alkali-earth metal chains, even at room temperature, that run perpendicular to the substrate dimer rows. It is found that the Sr rows form areas of (2x3) order for coverages theta about 1/3 hit after annealing at 800 degrees C whereas a (1x3) phase grows on top of this with theta greater than or equal to 1.0 ML coverage in agreement with LEED data. It was also observed that the (2x3) phase formation is critical to the Sr coverage and to the annealing temperature as well. The relationship between the (2x3) and (1x3) ordered structures has been investigated as a function of Sr coverage and annealing temperature.