PROVIDENCE — Do you want clean air, or clean water?

Environmental advocates, who want both, say that Governor Carcieri has forced that choice on the General Assembly with his plan to rescue the state’s bus system.

With the Rhode Island Public Transit Authority threatened with massive service cuts to cover a budget deficit, the governor has proposed shifting $2.2 million to the authority to maintain service, perhaps through the end of the fiscal year June 30. A number of environmental groups have pressed RIPTA’s case with the governor and the legislature because a stronger transit system would take cars off the road and reduce pollution.

The transit money would come from an obscure section of the state budget, the underground storage-tank fund. Administered by the state Department of Environmental Management and an appointed review board, the fund is used to respond to leaks and pay for the cleanup afterward.

Terrence Gray, the DEM’s assistant director for air, waste and compliance, said the change will cut the fund’s revenue in half and leave it with an annual deficit of about $1.25 million. There are about $1 million in claims on the review board’s agenda for its quarterly meeting March 12, which Gray said the fund can cover. But eventually, he said, the board will have to consider reducing or delaying reimbursements.

He said that the fund has another role, critical but infrequent: paying for an emergency response to leaks like the one in 2001 that contaminated wells serving 1,200 homes in Pascoag with MTBE, the gasoline additive.

By cutting revenue to the storage-tank fund, “The state could be gambling that nothing is going to go wrong,” said Paul Beaudette, president of the Environmental Council of Rhode Island and a member of the review board. The availability of the fund, he said, was important in responding to the Pascoag leak.

Amy Kempe, Carcieri’s news secretary, called the governor’s plan “a reasonable way to address an immediate need for RIPTA,” while allowing time to assess long-term funding sources for the authority.

“This helps with RIPTA while keeping the UST [underground storage tank] projects on track,” she said in an e-mail message. “RIPTA benefits and nothing changes for UST.”

Beaudette disagrees, calling it “a false choice” and saying that the governor has set “one component of the environment against another.”

Gray said most of the leaks involve gasoline and come from tanks at service stations.

Gasoline leaking underground causes two sorts of trouble, he said: it makes ground water undrinkable, and its vapor can penetrate cellars with unhealthy and possibly disastrous consequences.

The shift in money to RIPTA is contained in the governor’s proposed supplemental budget, which would amend the state budget for this fiscal year. The change would cut by half the amount of money from the state motor-fuel tax going to the storage-tank fund, redirecting it to RIPTA.

Adding to the unhappiness of environmental advocates is that the change could be permanent. Because the supplemental budget provision would rewrite the state law governing revenue from the gasoline tax, it would apply in future years, too, unless the legislature changed it back.

The governor’s move makes it difficult for environmental advocates to say much of anything.

“I can’t be supporting taking money out of one environmental fund to support another environmental fund,” said Chris Wilhite, director of the state chapter of the Sierra Club, an environmental group that has been vigorously pushing the governor to put more money into transit.

Gasoline breaks down into substances, including benzene and MBTE, that mix with water and travel with it underground, quickly contaminating water supplies, Gray said.

The first step in dealing with a leak is to empty the leaking tank. After that, cleanups become complicated and expensive. Gray said they often involve drilling test wells around the leak to learn which way the underground plume of gasoline is moving. Attempts are made to extract the contaminated water and treat it. The leaking tank is often dug up so that the heavily contaminated soil around it can be excavated and shipped off for disposal.

Tank operators must pay the first $20,000 of the cleanup cost and can then apply for reimbursement from the fund.

Without the reimbursement program, Beaudette said, the small, often family-owned businesses that run many service stations couldn’t afford the cleanups that are required.

“They would go bankrupt,” he said.

Gray said there are relatively few new leaks, four in 2007 and two in 2004, so most of the claims to the Underground Storage Tank Review Board are to pay the continuing costs of cleaning up past leaks.

That, Beaudette said, is because the present system works well.

“We haven’t had huge incidents because the UST regulations and functions are working well,” he said. “Part of that is the fund.”

blandis@projo.com