Yes you can using mutually referential namespaces. For example:
namespace rec X
open System
module B =
let m1 = A.hello()
module A =
let hello() =
printfn "Hello world"
Note though that this feature was built so that modules A and B could reference each other, and not just so that you can re-order things how you wish. It’s not recommended to use this feature just as a way to re-order your definitions. It can really mess with the type inference and give hard-to-understand errors and warnings