DENVER -- Attorneys for Gov. Bill Ritter and the state say school districts opted out of protections against property tax increases when they won voter approval to keep revenue beyond limits set by the state Constitution.

The argument came during Friday's closing statements in a lawsuit challenging a freeze on property-tax rates that generates more money for schools but blocks the tax rate from dropping in some school districts.

Opponents of the freeze approved last year by the Legislature and backed by Ritter argue the measure amounts to a tax increase, which requires voter approval.

But attorneys for the state say voters where the freeze applies have already backed allowing their school districts to keep revenue collected above constitutional limits.

Several school board members testified during the trial in Denver District Court that voters were told ballot proposals seeking relaxation of the Taxpayer's Bill of Rights wouldn't raise taxes. The assurances were sometimes part of the information the districts sent to voters.

Attorney John Mill, representing the Colorado Education Department, said those assurances weren't legally binding.

Attorney Richard Westfall, representing taxpayers challenging the tax freeze, said the votes by individual school districts weren't enough. He said a statewide vote is necessary because the Legislature's action altered the state school finance act, which applies to all 178 Colorado school districts.

District Judge Christina Habas indicated it could be several weeks before she issues a ruling.

The law passed last year is expected to raise an estimated $1.7 billion for education over 11 years by freezing property tax rates in districts with relatively low tax rates, blocking any declines for the foreseeable future. The freeze raises the tax bill for owners of property that increases in value.

Statewide, the increase is more than $117 million this year.

In some districts with the highest rates, the property tax rate will drop.