PROVIDENCE — The state’s transit system is on its own until January, when, its officials say, it will have to start cutting bus service by as much as 20 percent because of a large and growing budget deficit.

General Assembly officials and Governor Carcieri’s office gave no indication late last week that they will come up with more money for the Rhode Island Public Transit Authority by then, and a spokeswoman for Carcieri accused the authority of using scare tactics by discussing service reductions at all.

John Rupp, the new chairman of the authority’s board, said he is putting together the best arguments he can for more financing from the governor. One point, he said, is that unlike some other state costs, “RIPTA has expenses that can’t be deferred.” Its big expenses — diesel fuel, bus maintenance and payroll — have to be paid continually to keep the system operating.

Rupp said that doesn’t mean RIPTA can’t be improved by cutting expenses, administering its system better and perhaps eliminating some service. Overtime spending needs to be controlled better, he said, and the RIde paratransit program “needs a lot of work.”

However, Rupp said that by January, “if nobody’s committed to come up with money, we start cutting service.”

The legislature doesn’t convene until January.

Rupp said he is “guardedly optimistic that we’ll get through this crisis,” and that he believes that Carcieri, who appointed him, “is personally very concerned about this.”

“It’s a misconception,” Rupp said, “that the governor is not supportive of transit.”

Carcieri’s press secretary, Amy Kempe, however, repeatedly accused the RIPTA board of using “slash-and-burn” tactics in discussing service cuts, and called it an attempt to “scare people.” She said that “before they just slash and burn it would be better served if they would take a comprehensive look at how to operate more efficiently and to better serve the public.”

Kempe also objected to use of the term “service reduction,” saying that “maybe it’s a change in routes or it’s tweaking service and taking a comprehensive look” at the bus system “and seeing if there are some slight changes” that might help.

Asked whether any steps are being taken to deal with RIPTA’s deficit, Kempe said it’s “too soon to comment” because the budget process is at “the very, very beginning.” With the state government struggling with its own deficit problems, all state agencies have to operate more efficiently, she said, and “RIPTA should be no different.”

RIPTA administrators predicted trouble two months ago, saying in early July that sharply increasing diesel fuel costs were causing a deficit that could force service cutbacks affecting more than 160 bus routes. Authority officials said last week that the projected deficit is so big that even if bus service is cut back 20 percent starting in January, several million dollars of this year’s deficit would still have to be pushed forward into the next fiscal year, when RIPTA’s prospects are even darker.

RIPTA officials developed a detailed service reduction plan, which largely targets routes and segments of routes that are used the least. The plan was published in The Journal on Wednesday and is available on its Web site, www.projo.com, along with the schedule for public hearings on the cuts.

“The worst thing that could happen is for the service cuts to be adopted,” said Chris Wilhite, the executive director of the state Sierra Club chapter. He said that the state’s leaders “need to figure it out, and figure it out right now” so that RIPTA doesn’t have another fiscal disaster next year. He said that until they do, the bus system must be kept going even if it runs a deficit.

Rupp said that RIPTA can’t simply put off dealing with the situation. For one thing, he said, at some point, the authority would not have enough cash to pay its bills.

Kempe said that because the RIPTA board has not voted on the service reductions, it is “premature” to discuss the possibility. “The governor time and time again has supported RIPTA and continually supports RIPTA,” she said, “but has stated over and over again the importance of operating more efficiently.”

Spokesmen for the top officials in the state House and Senate referred questions about RIPTA’s situation to lower-ranking legislators.

A spokesman for Senate President Joseph A. Montalbano referred questions to state Sen. Joshua Miller, D-Cranston, a transit supporter. “There absolutely will be legislation” intended “to give RIPTA the funding it needs to grow” when the next General Assembly session begins in January, Miller said.

“I personally have an interest in it, the Senate policy office has an interest in it, the Senate fiscal office has an interest, and we’re working on solutions,” Miller said.

A spokesman for House Speaker William J. Murphy referred questions to Finance Committee Chairman Steven M. Costantino, D-Providence. Costantino said he’s “a little bit suspicious” about RIPTA’s figures, particularly its assertion that it moved from a balanced budget to a giant deficit in only a few months this spring. He also questioned RIPTA’s overtime costs, and wondered whether RIPTA’s explanation of its financial crash — primarily diesel fuel costs — explains its entire problem. But he said he’ll talk to his committee members about holding hearings on RIPTA’s situation soon.

It’s not that RIPTA and the board is facing a specific deadline, but rather, they say, dealing with a problem whose impact will increase with time. RIPTA officials said the more the agency puts off acting, the more service will have to be cut to close a deficit they estimate at $12 million for the fiscal year that began July 1. They say they expect to save enough to reduce that to about $10 million.

The authority can’t cut service without holding public hearings first, so the service cuts can’t go into effect before January, halfway through the fiscal year.

That would mean making roughly $20 million in service cuts during the last half of the year to cover the estimated deficit. Waiting longer would mean deeper cuts to make up the same amount.

blandis@projo.com