IQ test are fair, insists Prof. Arthur Jensen, a University of California psychologist, in an interview to be aired on "Prime Time saturday" on NBC next Saturday (10-11 p.m.). Monitor TV critic Arthur Unger reports that the Jensen segment could revive the recent controversy about the alleged genetic inferiority of blacks. For the past 10 years Professor Jensen has studied IQ tests in an attempt to evaluate their fairness. Since blacks consistently score 15 points lower than whites, the question of environment vs. heredity has become an explosive black-white issue. Now Professor Jensen has concluded that blacks are genetically less intelligent, and he expounds this controversial theory in a book, "Bias in Testing," to be published soon.