The slumping economy is changing the debate on O'ahu rail transit less than a month before voters decide on a City Charter amendment on whether to authorize Mayor Mufi Hannemann's proposed $3.7 billion commuter train from East Kapolei to Honolulu.

Increasingly, it's becoming an argument about jobs creation and the economic impact as much as traffic relief.

Rail opponents, who have always argued that transit costs too much for O'ahu's tax base to absorb, say this is even more true now that tourism is in major decline, government revenues are sharply down and credit is tight in what appears to be a protracted economic downturn.

Hannemann's opponent for mayor, Councilwoman Ann Kobayashi, says a rail system would "cause severe economic hardship for O'ahu."

Backers of the train argue the opposite, that rail construction and the expected real estate development around train stations is just the economic boost we need to carry us back to prosperity.

Some enthusiastic advocates for rail call it a New Deal for Hawai'i, drawing comparisons to the federal public works spending that helped lift the United States out of the Great Depression.

Voters will have to decide which view they trust more from the gut than from accepted facts because there are no hard numbers on what it will end up costing to build and operate the most expensive public works project in Hawai'i's history.

The current estimated cost of $3.7 billion for the initial 20-mile line is based on 2006 dollars and is expected to rise to about $5 billion when adjusted for inflation.

Adding extensions to West Kapolei, the airport, Waikiki and the University of Hawai'i that would be necessary to make the transit system fully functional would likely bring the cost closer to $6.5 billion, which could go much higher if we experience the average 40-percent cost overruns seen in other recently built train systems.

The half-percent O'ahu excise tax enacted to pay for rail and hoped-for federal funds will bring in an inflation-adjusted $5 billion at most, and the city has given little clue as to where money to pay for any additional costs would come from.

Nor has the city addressed in any detail how it'll pay for operation and maintenance, currently estimated at about $1 billion for the first decade after construction is completed.

Beyond the cost of rail itself, voters have to consider how it'll limit our ability to pay for other high priorities. If the $1 billion cost for the sewage-treatment upgrades the federal government wants would bankrupt Honolulu, as Hannemann claims, it's only because of the money rail is tying up.

On the other side of the argument, there's no denying government spending on public works construction is a key weapon in reversing a sour economy.

Gov. Linda Lingle, who sends out mixed signals on her view of the O'ahu rail plan, is herself planning to push out $1 billion in state construction projects in the next year, saying construction spending is an important "multiplier" in the economy.

Former Gov. Ben Cayetano, who opposes rail transit, also moved to drastically step up state construction spending in Hawai'i's last economy slump.

Talking about jobs and economic stimulation as much as traffic relief puts the discussion on a more candid footing; from the start, primary backers of rail have been construction trade unions and contractors who want the work.

As a construction worker who commented on my primary election blog put it: "I care less what we build, what it's for or if it works. My concern is job security."

That's as honest as this debate gets.

David Shapiro, a veteran Hawai'i journalist, can be reached by e-mail at dave@volcanicash.net. His columns are archived at www.volcanicash.net. Read his daily blog at blogs.honoluluadvertiser.com.