As cities swallow countyside, two upcoming conferences will consider ways to protect open and agricultural land from urban growth. Montanans meet in Helena Nov. 20-21 for Big Sky or Big Sprawl? Montana at the Crossroads: Montana's First Statewide Summit on Growth. Call or write AERO, 25 S. Ewing, Suite 214, Helena, MT 59601 (406/443-7272), or e-mail mlincoln@desktop.org. Keep America Growing will take the national view in Philadelphia June 6-9. Contact KAG Conference, 123 Brick Church Road, Fairfax, VT 05454, e-mail delaney@together.net, or check out the conference's Web site at www.farm