One month before national elections, the listless Dutch Liberal Party seems likely to lose perhaps a third of its 36 seats in the 150-seat parliament. Its troubles only increased when this month's Dutch edition of Playboy hit the newsstands. The magazine showed two Liberal Party officials partying very liberally indeed. One shot shows Party Secretary Arnoud Cevaal, 37, sitting on one of the classic green benches inside the stately parliamentary assembly hall in the Hague. But Cevaal's mind is clearly not on affairs of state, since his hand is busy exploring the bared behind of Lorette Welter, 30, personal assistant to a Liberal member of parliament. In the pages that follow, Cevaal and Welter are shown showering, bubble-bathing and sleeping together in the altogether. When an affronted parliamentary chairman demanded an explanation, the gladhanding lovers turned suddenly cool. Welter said that she merely wished "to give politics a romantic flavor." Cevaal, asserting, somewhat needlessly perhaps, that the couple had "nothing to hide," said that they had volunteered to pose, without charging a fee, in order to show that "politicians are human too." Unimpressed by those explanations, the Liberals last week decided to fire both of its exposed members.