Things are getting heated in Kings County over the city's decision to transform a lane of traffic on Prospect Park West into a two-way bike path. This morning, protesters and supporters faced off in dueling rallies. Advocates say it has increased safety for bikers and reduced speeding cars. Critics, including the senior citizens from the area, complain about near misses with bikers, and don't understand why they can't use the perfectly good bike lane already in the park. The quiet rage is contagious: Chuck Schumer's wife, Iris Weinshall, a former Department of Transportation commissioner who lives on Prospect Park West, hung up on a Daily News reporter who just wanted to know if she was attending the rally. But borough president Marty Markowitz has identified the real problem: the Department of Transportation's desire to experiment, using Brooklyn as a "guinea pig," with emulating that hedonistic bike-worshipping capital to the east. "What is our objective in this city? To stigmatize the use of cars? To make it difficult to park? Do we want Brooklyn to replicate Amsterdam?"