McLardy is at 14-under 130 after 36 holes. Nick Dougherty (64) is a stroke behind, followed by Joakim Backstrom (70), Markus Brier (69) and Alvaro Quiros (67) at 132. More than 10 hours of play have been lost since the tournament began because of torrential rain.
Backstrom shot a course-record 62 Thursday but didn't play a hole Friday because of rain. He dropped shots on the sixth and 18th holes in the second round.
McLardy, who resumed his rain-delayed second round at 7 under after five holes, had six birdies on the back nine. Dougherty, a protege of six-time major champion Nick Faldo, matched his lowest European tour score with the day's best round of 64.
Quiros eagled the 513-yard ninth. Brier, who shot a 63 Thursday, had five birdies and two bogeys.
Defending champion Francesco Molinari (69) is 8 under while Tom Lehman (68), last year's American Ryder Cup captain, is 6 under. Lehman is playing his first Italian Open on a special invitation.