The method comprises the phases of: knitting at least one part (5 A, 5B) of the body (1) with reciprocating motion of the two cylinders of a double-cylinder machine; —knitting the leg pieces (9 A, 9B) with a continuous rotational motion of the two cylinders (11, 13), a first leg piece being knitted by a first of said cylinders and a second leg piece being knitted by a second of said cylinders. It is provided for an arc of needles (C) to be maintained temporarily inactive on each of said two cylinders while knitting said at least one part (5 A, 5B) of the body (1) with reciprocating motion. Furthermore, it is provided that the temporarily inactive needles are set to work at the end of the knitting of said at least one part (5 A, 5B) of the body (1) with reciprocating motion, thus forming an interknitting line (CC) for joining the two leg pieces (9 A, 9B), then continuing the knitting with continuous rotary motion with all the needles (15) of both the cylinders (11, 13).