UPDATE 1-Mexico's ICA to bid for $18 bln in projects

(Updates with projects, tax details, share impact)

MONTERREY, Mexico, Oct 23 (Reuters) - ICA, Mexico's top builder, aims to bid for $18 billion in projects over the next 12 to 18 months, but also expects its debt to increase, the company's chief financial officer said on Friday.

Alonso Quintana told analysts ICA (ICA.MX)(ICA.N) has strong growth potential as the Mexican government moves forward with major infrastructure projects including the Atotonilco water treatment plant and the Mexico City light railway.

But the company's debt is a concern to some investors. ICA's net debt rose 87 percent between September 2008 and September this year and is set to keep rising as the company takes on more bank debt to finance its projects.

"Net debt should increase maybe 3 to 4 billion pesos in the next quarter," Quintana told analysts.

Shares in ICA in New York fell 1.51 percent to $10.47 after rising in early trade and slipped 0.09 percent to 34.05 percent in Mexico City.

Quintana also warned planned tax hikes in Mexico could also hurt the company. Mexico's lower house of Congress passed this week a watered-down version of President Felipe Calderon's tax reform proposal; and for ICA, the bill could force it to pay taxes on its holding company as well as its various units.

"There is the potential that it could come out damaging companies like us," Quintana said.

Senators are now revising the plan, which also includes raising value-added tax, along with levies on beer, telecommunications, gaming, and high-income earners. (Reporting by Gabriela Lopez, editing by Gerald E. McCormick)