ALA, ARL prefer clarification to legislation

The 1709 Blog thanks Chris Torrero for drawing its attention to this note on District Dispatch ("News for friends of libraries from the ALA Washington office") on the US Copyright Office's report, which recommends some tinkering with US copyright law. Says the note

"The United States Copyright Office has recommended that pre-1972 sound recordings should be protected by federal copyright law in its Report on Federal Copyright Protection for Pre-1972 Sound Recordings. Currently, these older sound recordings are protected by state laws under which copyright exceptions such as library and archival preservation and fair use are uncertain. This uncertainty leads to caution on the part of music librarians and archivists to actively preserve sound recordings— some in fragile or obsolete formats and extremely rare. 

The American Library Association (ALA) and the Association of Research Libraries (ARL) argued in their comments to the Copyright Office that—while federalization of pre-1972 sound recordings would help clarify that library and archives are free to preserve sound recordings— an equally effective solution to the problem be supported. Since any legislative change to the copyright law is fraught with uncertainty, a simple clarification from the Copyright Office that fair use doctrine applies to state-protected works would be more definite. ...".

It seems curious to this blogger that a "clarification" from the Copyright Office that fair use doctrine applies to state-protected works should be more definite than, or preferable to, legislation. What is the legal status of such a clarification? Is it immune from challenge and resistant to interpretation? And is there no question regarding the power of the Copyright Office -- a Federal body -- to make pronouncements regarding state law?  Some clarification from US readers would be appreciated.