OREGON CITY -- Clackamas County light rail opponents

that could resonate for decades.

Initiative Measure 3-401,

, requires countywide voter approval before officials can spend money to finance, design, construct or operate any rail lines in the county.

It's unclear what effect the measure will have on the controversial Portland-Milwaukie light rail extension, the $1.5 billion project at the heart of the battle. The line is already under construction, and on Friday

for its share of the project.

But if left intact after possible legal challenges, the

, including possible high-speed passenger rail connecting Seattle and Eugene. Early discussions have mentioned possible high-speed routes that would traverse parts of unincorporated Clackamas County. Similarly, efforts to expand freight rail for industrial and commercial uses could also be limited.

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Supporters of the measure, who generally oppose the

, said the initiative is about giving voters a voice on whether to support what they see as an unpopular, debt-financed project.

and authorized a contract to finance it, but it was never put to a countywide vote.

"This is a clear mandate for the citizens of Clackamas County that they want the opportunity to vote on light rail and rail projects," said Jim Knapp, the original sponsor of the measure. "The county commissioners aren't listening."

Approval of the measure could lead to protracted legal battles.

to finance the project without voter approval. A successful challenge could mean the measure would be in effect before county officials could reauthorize payment.

"We're just going to weigh up our legal options, see what we have," said Knapp, who declined to elaborate on those options. "It's never over. It's not over when they violated our right to vote."

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Rail supporters argued the measure would require costly special elections for administrative decisions. They also say that the initiative process is by law intended for legislative matters, not administrative actions.

The chairwoman of

, a newly formed group that opposed the measure and supports regional planning and transportation efforts, said again Tuesday night that the group is prepared to challenge the measure in the courts, even though the county has paid TriMet for its Orange Line tab.

"

," Eleanore Hunter said Monday. "I feel the county commissioners deserve our full support to be able to do their full job. I'm not willing to let the governance of Clackamas County be eroded by a minority of people."

County chairwoman

said the measure would do little to stop a large, interstate project such as high-speed passenger rail, though it "makes it hard for the county to be an active participant in where that goes through the county."

"Obviously if you're doing high-speed rail from Seattle to Eugene or San Francisco, it's going to come through Clackamas County," she said. "Interstate 5 came through whether local jurisdictions wanted it or not. High-speed rail is one of those projects: It's bigger than Clackamas County by a long shot. Clackamas County does not have the ability to stop something like that."

, including seeking that it be declared unconstitutional. Commissioners also said that if the measure passed

without first obtaining voter approval.

The passage of Measure 3-401, championed by conservatives in the county, could propel two Republican candidates to victory in the Nov. 6 general election races for nonpartisan county commission seats.

.

The conservative momentum from this special election, however, will be met with what is expected to be a heavy Democratic turnout for President Barack Obama. That could prove decisive for Lehan and Commissioner Jamie Damon, both Democrats who support the light rail project and are fighting to retain their seats.

A similar initiative in King City, Measure 34-199,

.

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