Car sales in Rhode Island declined precipitously in the three months that ended Oct. 1, based on data from the state Department of Revenue, which collects a tax on the sale of new and used cars, trucks and other vehicles.

In July through September last year, the state received $25.5 million. In the same period this year, the state’s take was $20.8 million, a decline of 18 percent. A closer look at the numbers reveals a downward trend. July was off 15 percent from the previous year; August, 17 percent; and September, 23 percent.

Two economic forces have driven vehicle sales down: consumers have less money to spend and more trouble borrowing.

“If your credit is less than great, you may have a little bit more of an issue than you had in the past,” said Barbara Saccucci, general manager of Saccucci Auto Group in Middletown. “They may be less welcoming as far as rate goes. They’re more strict with people who have less than great credit.”

The slump in auto sales and the difficulties in borrowing money to buy a car stretch beyond Rhode Island’s borders, according to Gary S. Sasse, the state’s revenue director. “It’s reflective of what’s happening in the national economy.”

Indeed, major automakers reported a bleak September for U.S. sales, according to Bloomberg News.

Ford Motor Co. reported sales of cars and light trucks down 35 percent this September compared with last year, according to Bloomberg. Toyota Motor Corp.’s sales dropped 32 percent in the same period. Honda Motor Co. fell 24 percent. General Motors Corp. declined 16 percent, the shallower dip attributed to the company’s “employee pricing” discounts. Nissan Motor Co. fell 37 percent.

“It’s a credit story industrywide,” Tom Libby, a market analyst at J.D. Power & Associates, told Bloomberg. “Also, there is a psychological impact of all the news about banks in trouble. If people can wait to buy a car, they’ll wait.”

While national numbers on car sales have been published, similar figures for Rhode Island are more elusive.

R.L. Polk & Co., a national automotive market research firm, tracks numbers state by state, but that data generally is not available for two to four months after the financial quarter ends, according to a company spokeswoman.

The best measure available for Rhode Island is the sales-tax collection, though it is an imprecise indicator because the Division of Motor Vehicles collects the tax for a variety of transactions.

On new vehicle purchases in Rhode Island, the buyer pays 7 percent of the sale price. For used vehicles, the 7-percent tax is calculated based on the book value or the sale price, whichever is higher.

For out-of-state purchases, Rhode Islanders are required to pay a use tax equal to the difference between the Rhode Island tax and the tax in the state where the vehicle is purchased. Typically, this is the 2-percentage-point difference between Rhode Island’s and Massachusetts’ sales taxes.

The tax applies whether the sale is private or through a dealer.

The drop in Rhode Island sales-tax collection could indicate fewer new vehicles being bought, a migration to used-car purchases or a combination of both.

pparker@projo.com