Marine Corps Organization
Marine Expeditionary Force (MEF): The MEF is the principal war fighting element in the active force structure of the Marine Corps and is usually commanded by a lieutenant general. The size and composition of a deployed MEF varies depending on the needs of the mission.
Marine Expeditionary Brigade (MEB): A MEB, usually led by a brigadier general, is built around a reinforced infantry regiment, an aircraft group and a Service Support Group. Capable of rapid deployment and employment via amphibious or airlift methods, it is the first echelon of a Marine Expeditionary Force.
Marine Expeditionary Unit (MEU): The smallest task force unit, the MEU has approximately 2,200 personnel and is built around a reinforced infantry battalion, a composite aircraft squadron and a support group. It is commanded by a colonel and is routinely deployed with an Amphibious Ready Group. The ground element of a MEU is a Battalion Landing Team (BLT), comprised of a reinforced infantry battalion of approximately 1,200 Marines, including three Rifle Companies. The aviation unit of a MEU is a reinforced medium helicopter squadron.
http://www.montney.com/marine.htm
BTW, II MEF's site described a MEF's force structure as more than 47K, so it sounds like it's essentially the same size as I recall.