A task force of metro Denver mayors agreed Thursday that RTD should ask the legislature to give it a limited option to seek a second FasTracks sales tax hike this year.

While the mayors aren't ready to endorse a second increase of up to four-tenths of a cent for the cash-strapped $7.9 billion transit program, they agreed that lawmakers should clear the way for RTD to ask voters' approval if officials believe that's the only way to build the new rail lines.

RTD, unlike most other public bodies, cannot on its own put measures on the ballot. It needs a say-so from the General Assembly. In 2002, lawmakers passed a bill that allowed RTD's FasTracks sales tax hike to go to metro Denver voters but only if it got there by citizen initiative petitions.

If RTD doesn't get permission for a vote before lawmakers adjourn in May, it would have to wait until next year.

The mayor's task force is working with RTD to find ways to close a $2.1 billion funding gap. It plans to reach a recommendation for RTD by late March, but mayors were reluctant to endorse a second tax hike because they don't yet have all the numbers from RTD.

The transit agency is recalculating project costs in light of recent downturns in construction prices, hoping the $7.9 billion figure will shrink. But still, the deficit may grow because sales tax revenue, which pays for much of it, is lagging.

Thornton Mayor Erik Han- sen was the most skeptical, declining at first to join in a consensus to approach the legislature until he had more information.

"Why would we do this?" he said. "We don't have the numbers yet."

In the end, he joined the other mayors after conditions were put on the table.

They include requiring the measure to make the ballot through petitions, using the new tax only for construction and ending the new tax when bonds are paid off.