Fueled by huge jumps at Fannie Mae and Freddie Mac, issuance of agency-backed CMOs and REMICs skyrocketed during the first quarter. A hefty $39.55 billion in new agency REMIC securities were issued during the first part of 2001, a refi-aided 136.2 percent jump from the $16.75 billion issued during the same period last year. Fannie Mae and Freddie Mac REMICs accounted for the