The Sierra Club’s national board of directors is opposing a major swap of public and private land in Washington state, which was approved by the Senate last week. The board heard last week from residents of Randle, Wash., who live near a parcel of national forest called Watch Mountain that would be turned over to the Plum Creek Timber Co. The residents fear the company would clearcut the steep land above their town. Until now, the local chapter of the Sierra Club had supported the trade as the best way to acquire sensitive forest lands east of Seattle, but now the national directors say the deal must be amended to keep certain parcels in public hands. The board also decreed over the weekend that no local Sierra Club chapter can back a public land trade unless it gets approval from national headquarters, an action clearly aimed at the Seattle-based chapter, which has worked for more than 20 years to put together the swap.