Gun manufacturers and retailers throughout New England are struggling to keep up with surging demand as buyers, worried their options may soon be limited, snap up firearms and ammunition.

Shops say they have sold out of many popular gun models, including variations of the AR-15-style rifle used in last month's mass shootings in Newtown. Some retailers have resorted to capping the number of bullets customers can buy in an effort to preserve dwindling inventories, or taken to marking up prices.

The sharp increase in sales is fueled by the looming prospect of greater controls on firearms. Proposals to further restrict or regulate ownership are pending nationally and in Massachusetts.

The surge in purchases can be gauged by the wave of background checks required for prospective gun buyers. Nine of the 10 busiest days for background checks ever recorded by the FBI were in the past two months. In December alone, the agency performed 25,251 checks for would-be buyers in Massachusetts - an increase of 73 percent from a year earlier.

"People are afraid of what Obama is going to do," said Ted Oven, owner of Northeast Trading Co. in North Attleborough. "People who were going to buy in the spring are rushing to buy now."

On a recent day, the store's display wall featured only two AR-15-style rifles. Oven said about 60 customers have requested similar guns that have yet to arrive. He also submitted orders for $1 million worth of guns and accessories at a trade show in Connecticut this month, but no one could guarantee a delivery date.

Johnny Donnelly, a firearms instructor from Woburn, said he had to add a second four-hour firearms safety class on Sunday to accommodate demand from new gun owners.

"It's definitely the highest interest I've ever seen," said Donnelly, who hopes to open a gun store in Massachusetts this year. "Even people I didn't know were interested in firearms are talking about it."

Some gun clubs are also worried about finding enough ammunition for training programs, said Jim Wallace, executive director of the Gun Owners' Action League in Northborough, the Massachusetts state affiliate of the National Rifle Association.

The increase comes at a time when many manufacturers already were having a difficult time producing enough guns and bullets to keep stores fully stocked.

Smith & Wesson Holding Corp. had $332.7 million worth of backlogged orders at the end of October, nearly double its backlog from a year earlier. The Springfield company, which introduced 11 "modern sporting rifle" models - semiautomatic guns like the AR-15 - in fiscal year 2011, recently said it planned to boost production, with both outside vendors and expansion of its own facilities.

Stag Arms, a maker of AR-15-style rifles in New Britain, reported this month that it has two years of back orders for the guns and related parts.