A hotly contested mayor's race is claiming the spotlight as Quincy prepares to hold its preliminary election on Thursday, Sept. 24. Mayor Thomas P. Koch, finishing his fourth term, is vying with former mayor William J. Phelan, City Councilor Doug Gutro, and School Committee member Anne Mahoney. The top two vote-getters will move on to the Nov. 3 city election. Two other races are featured in the preliminary, contests for ward councilor in wards 2 and 3. In Ward 2, incumbent Brad Croall is competing with first-time candidates James M. Connors and Gulistan M. Malik. In Ward 3, three candidates are contending to replace retiring incumbent Kevin F. Coughlin. They are Ian Cain, Karl Roos, and Sandy Verhault. Roos and Verhault, a former member of the Mayor's Commission on Women, both previously ran unsuccessfully for School Committee. Cain is making his first bid for office. Voting hours are 7 a.m. to 8 p.m.