Mr Ritchie

The records for your ancestor are maintained in the National Archives, Record Group 109. There are ways to access them on-line if you have appropriate memberships.

In the Andrew B. Booth 3-volume listing of Louisiana Confederate soldiers, Levi B. Robertson is listed and can be addressed at the following:
1) http://search.ancestry.com/cgi-bin/sse.dll?db=confed&rank=1&new=1&so=3&MSAV=0&msT=1&gss=ms_r_db&gsfn=Levi+B&gsln=Robertson&uidh=x9g (requires a www.ancestry.com membership)
2) http://www.lascv.com/b67.html (Louisiana Sons of Confederate site - no membership needed)

For his Confederate Service Record (CSR), you will need to go to a National archives branch or you can use www,fold3.com which requires a membership. You may also be able to access some of his US Army record on this site. In the CSR, he is listed as Levi B. Robinson, not as Levi B. Robertson.
1) http://www.fold3.com/image/#271|77454739

You can also go onto the National Archives and Records Administration and copy a form which can be used to order his military services records (Union and Confederate). You can also contact the Louisiana CW message board webmaster for a researcher contact for National Archives research, for which there is a fee.

Hope this helps

Don Parker