Rodney J. Blonien, undersecretary of the Youth and Adult Correctional Agency, who is generally credited with rescuing Gov. George Deukmejian's ambitious prison construction program from disarray, has resigned his post to join a private law firm, Deukmejian announced. The governor immediately named Chon Gutierrez, a long-time trouble-shooter for the Administration, to head up the $2.1-billion prison program, the largest in state history. In accepting the resignation, Deukmejian praised Blonien, 40, for successfully completing work on 9,000 additional prison beds since he assumed the job in 1983. Gutierrez, 42, formerly deputy director of the state Department of Finance, has worked as a deputy director of the California Youth Authority and as head of the Office of Economic Opportunity. Gutierrez, a Democrat, will be paid $78,495 annually.