Fluor Corp., the Irvine-based oil services company, said Friday that chief financial officer George W. Mefferd, 59, will take early retirement, effective June 10. Mefferd, who has been with Fluor for 12 years, also is resigning from the board of directors. He said his retirement is "purely a personal decision." Mefferd said he had been considering leaving Fluor for some time but stayed "until the restructuring of the company was accomplished." A Fluor spokesman said no successor has been named.