I am looking for the title of a poem, and a place where I can find it.
 I am almost certain that it is by Archibald MacLeish (1892-1992).  It
is less than a page long.  It contains the phrases "the steps that men
can read on mountains" "a victor's perfect [or perhaps "endless"]
grace" and "perfect weather on the perfect creatures the world grows."
 The first part is addressed in second person to a woman, the last
contains these phrases in a wider description of the world.  I have
only seen this poem in the Jewish prayer book "The Gates of Prayer,"
used in Reform synagogues, I could not find it in MacLeish's collected
work.  Any help on tracking this down would be appreciated.

I do not believe the poem you are looking for was written by Archibald
MacLeish because he only wrote 10 poems:
An Eternity  
Ars Poetica
Baccalaureate
Dr. Sigmund Freud Discovers the Sea Shell 
Poem in Prose
The End of the World
The Snowflake Which Is Now and Hence Forever
The Too-Late Born 
Two Poems from the War  
You, Andrew Marvell  

None of which mention the phrases you are looking for. 
(http://www.poemhunter.com/archibald-macleish/poet-6626/ )

Not true, he wrote hundreds of poems as well as longer works.  Poem
Hunter is not an accurate list of all works.