A STUDY OF THE THREAT TO LICENSED NUCLEAR FACILITIES REVEALS THAT THE TYPES OF TERRORISTS MOST LIKELY TO POSSESS THE REQUIRED COMBINATION OF SKILLS AND MOTIVATIONS NECESSARY FOR NUCLEAR TERRORISM INCLUDE FOREIGN INTELLIGENCE AGENTS AND DOMESTIC INSURGENTS WITH MILITARY TRAINING. SUCH PERSONS ARE STRONGLY IDEOLOGICAL, BUT QUIET AND UNOBTRUSIVE IN DEMEANOR. WHILE THE FOREIGN AGENT IS CHARACTERIZED BY RATIONALITY AND OBJECTIVITY, THE DOMESTIC INSURGENT IS PASSIONATE AND INSTINCTIVE. ALMOST ALL AMERICAN DISSENT IS CONSPICUOUS, BUT WHEN DIRECT CONFRONTATION WITH AUTHORITIES DRIVES OPPONENTS UNDERGROUND, THEN TERRORISTS BECOME MORE DANGEROUS. IN ATTACKING A NUCLEAR INSTALLATION, SUCH TERRORISTS WOULD REQUIRE THE SERVICES OF TECHNICAL SPECIALISTS AND A DEDICATED CADRE THAT MIGHT NOT KNOW THE IDENTITIES OF THOSE WHO PLANNED THE ATTACK. IN ADDITION, SUCH AN ORGANIZATION WOULD PROBABLY HAVE CONNECTIONS WITH A LONG-STANDING TERRORIST GROUP. SIGNIFICANT QUANTITIES OF NUCLEAR MATERIAL HAVE ALREADY BEEN STOLEN, AND MANY NUCLEAR FACILITIES ARE VULNERABLE TO ATTACK. INCREASED SECURITY COULD LESSEN THE CHANCES OF TERRORIST SUCCESS. REFERENCES ARE PROVIDED. (TWK)