Backgrounds should include some experience in federal law enforcement of corporate crime, especially violations in the areas of scientific research and environmental pollution. Some characters (probably friendlies) should have scientific or medical credentials in organic chemistry, biological research and related fields. The ability to swim and scuba dive, and operate and sail a boat will presumably come in handy. It is also possible to make characters involved with Delta Green from Hawaii's own Z-Cell, either from local law enforcement or Hawaii's large military presence (which happens to be riddled with Majestic plants).
Please note that I use a variant cell structure in which alphabetical order does not necessarily indicate senority or proximity to A-Cell.
GURPS Delta Green
Player are to contruct their Characters using 150 points, with 45 points in Disadvantages and Quirks. The GURPS Lite rules are available for free download (in .pdf format) and may come in handy for those without full access to GURPS. The following packages are advisable:
Delta Green Agent : 0 point package
Agents must take Delta Green as a 50 point Patron (Reasonably Powerful, provides equipment, has special abilities and appears on a 12 or less) and Majestic as a 30 point enemy (Extremely Powerful, appears on a 9 or less). DG requires a -10 Sense of Duty to "save humanity from the Mythos", a -10 Extremely Hazardous Duty on a 6 or less, and a -15 point Secret (Member of an Illegal Government Conspiracy). This leaves 15 points to spend on Federal Law Enforcement powers (10 points) and one level of adminstrative rank (FBI Special Agent), or three levels of military or administrative rank, or some combination thereof. Agents get this package above and beyond their point quotas.
Delta Green Friendly: 0 Point package
Friendlies only pay 25 points for Delta Green's Patronage (same as Agents only DG appears on a 9 or less). They still must take the Secret (even if possessed of the -10 point Delusion: "Delta Green is an official government agency"), the same Extremely Hazardous Duty as Agents (on 6 or less), but do not have to take the sense of duty nor do they receive Majestic as an Enemy unless Delta Green is compromised, in which case Majestic becomes a -60 point Enemy that appears on a 12 or less. Friendlies get this package above and beyond their point quotas.
Skill packages and much helpful material concerning the FBI can be found in GURPSnet's X-Files conversion.