North-south strip 4000 ft long, later extended to nearly a full mile ("Finding Amelia, pg 17). Northeast-southwest strip 3000 ft long. East-west strip 2400 ft, and aligned with the prevailing winds. All were 150 ft wide. I think I read later on that the 2400 ft strip was extended some more, but a quick perusal didn't find it.
(later edit - these are the figures for Howland. Lae had a 3000 foot strip. Sorry 'bout that)