  We introduce the concept of conformal spin gradation of the untwisted affine
Lie superalgebra $\hat A(n-1| n-1)^{(1)}$ to study the $W\hat A (n-1|
n-1)^{(1)}$ Miura transformation. We show that the essential of $\hat A(n-1|
n-1)^{(1)}$ may be read from the conformal spin gradation of the canonical
vector basis of the $SL(n| n)$ vector representation space $V_{2n}$ and a
spectral parameter $\mu$. We give the generic formula of their conformal spin
weights. Then, we set up the fundamentals of a manifestly $N=2 U(1)$ Lax
formalism leading to a manifestly $N=2 W\hat A(n-1| n-1)^{(1)}$ Miura
transformation. Its explicit form is obtained and is shown to have a similar
structure as in the N=0 case. Both $N=0 W\hat A(n-1)^{(1)}$ and $N=2 W\hat
A(n-1| n-1)^{(1)}$ Miura transformations involve $(n-1) N=0$ and N=2 conserved
currents with integer conformal spins. The leading cases are discussed. Using
the U(1) charge of the N=2 algebra, we develop also a new method of
constructing N=2 superfield realizations of the N=2 higher spin supercurrents.
Among other results, we find that in general there are three series of $(n-1)$
higher conformal spin N=2 supercurrents. The usual N=2 super $W$ currents are
the only hermitian ones. At the $n=3$ level, we find a new Feigin Fuchs type
extension of the conformal spin one N=2 supercurrent. Such a feature, which has
no analogue at the $n=2$ level, is also present for $n>3$. Finally, we give the
N=2 superfield formulation of the N=2 Boussinesq equation and its
generalization involving complex N=2 supercurrents.
