The U.S. Citizenship and Immigration Services (USCIS) would administer any "guest" worker or immigration "reform" (amnesty) scheme. However:

But in recent months, U.S. Citizenship and Immigration Services (USCIS) officials have determined that the troubled, $2-billion-a-year agency is unable to effectively manage its existing work, much less a flood of new applications.

A report released Dec. 20 by Homeland Security Inspector General Richard L. Skinner cited a long list of setbacks and concurred with internal USCIS reviews that the bureau "lacks the processing capacity, systems integration and project management resources needed to manage a potential increase in workloads."

...Many legal immigrants already face years-long waits when they apply for green cards, often a first step toward obtaining citizenship.Another 100,000 names submitted to the FBI for background checks have been on hold for a year or more. Congressional auditors recently reported that 14 immigration offices had lost track of 111,000 files as of July...

Related:
"[USCIS] Whistle-blower let go"
"Terrorist screening missed 75% of time"
The Senate amnesty: an "Administrative and National Security Nightmare"
Whistleblower: USCIS broken, infiltrated by operatives of hostile foreign countries
USCIS director: Senate amnesty timeline is not "practical"
GAO report shows how "guest" worker schemes would fail miserably