Tiffany & Co., seeking to expand its presence in Orange County, has filed a lawsuit against South Coast Plaza, claiming the mall prevented the tony New York jeweler from opening a store at Mission Viejo Mall, which is undergoing a $150-million renovation in a move to position itself as an upscale shopping center in the burgeoning southern part of the county. Tiffany says in its suit that South Coast Plaza balked at its request to open a store in Mission Viejo Mall, invoking a non-competition clause in the jeweler's lease that is "illegal and unenforceable." The suit, filed Wednesday in Orange County Superior Court in Santa Ana, is seeking $1 million in damages. Tiffany, which opened its shop at South Coast Plaza in Costa Mesa in 1988, also asks the court to stop South Coast Plaza from enforcing the lease. The mall's attorneys are examining the lawsuit, said spokeswoman Debra Gunn Downing, who declined to comment further.