Although sales rose 7 percent from a year ago, the seasonally adjusted annualized selling rate fell to 11.5 million, below the level of 11.8 million in May. The selling rate, a closely watched measure of the industry’s health, topped 13 million in February, March and April.

“We continue to believe the economy will recover from the current short-term slowdown into the second half of the year,” Don Johnson, General Motors’ vice president for United States sales operations, said in a conference call. “Some consumers have decided to sit on their hands and delay purchases, but we view this as temporary.”

Sales fell 21 percent at Toyota and Honda — it was the worst June for both companies since 1997 — and 8 percent at Subaru.

Those declines contrasted with gains of 11 percent by G.M., 10 percent by Ford and 30 percent by Chrysler, which outsold Toyota for a second consecutive month. The Detroit carmakers accounted for more than half of sales for the first time since September 2008.

It was the 15th consecutive month that Chrysler posted a year-over-year gain and the company’s best June since 2007. Sales by its Jeep sport utility vehicles were up 74 percent last month, and popular new models introduced since its 2009 bankruptcy helped increase sales in the first half of the year by 20 percent.

Sales of the Toyota Prius fell 61 percent, to 4,340, an average of fewer than four per dealer and the lowest total for a month since September 2004, as the automaker struggled to restore availability after the earthquake and tsunami in Japan in March. Toyota said it had just 1,400 of the cars left in inventory but that 36,000 were on the way to the United States this summer.

Toyota officials said inventories were improving considerably as many plants returned to normal production levels and that the company would advertise more aggressively in July to ensure customers knew dealers had cars to sell.

“Consumers had the perception that they would simply not be able to find the car they’re looking for, and even if they did that they would have to pay an arm and a leg for it,” Jesse Toprak, vice president of industry trends and insight at TrueCar.com, which tracks vehicle pricing and sales. Though availability is better than many shoppers might realize, he said, “it’s not going to be before the fourth quarter that we see a decent inventory mix for the Japanese automakers.”

For the first half of 2011, Toyota’s sales were down 4 percent from those in the period a year earlier, and Honda’s sales were up 3 percent. Chrysler’s sales were 21 percent higher from January through June, G.M.’s sales were up 17 percent and Ford’s rose 9 percent.

As in May, cars made by G.M. and Ford outsold their long-dominant rivals at Toyota and Honda. The Chevrolet Cruze, a compact car introduced by G.M. last year, was the nation’s top-selling car in June. G.M. and Ford executives said buying patterns shifted toward larger vehicles later in the month as gas prices dropped in much of the country.

Toyota responded to its inventory shortages by pulling many discounts, but it introduced new deals in June after traffic at dealerships slowed sharply.

“Things actually were going along pretty well in March and April, and the shortage hit us badly,” said Earl Stewart, owner of Earl Stewart Toyota in North Palm Beach, Fla.

His dealership sold 88 Prius cars in March but only 12 in June before running out. Mr. Stewart said his new-car department was profitable early in the year but lost money in May and June, as sales went from an average of 265 a month to about 140 in May and then 180 last month.

“They put the incentives back on, but you can’t un-ring a bell,” Mr. Stewart said. “The message got out to a lot of people. It had a psychological negative impact on the Toyota buyer.”

To keep shoppers from sitting on the sidelines — or worse, choosing a competitor’s readily available vehicle — Toyota and Honda have begun offering incentives to people who order a car even if it does not arrive at the dealership for several months. Normally, incentives are available only on vehicles that are in stock or delivered in the same month.

“Fortunately for them, Honda and Toyota customers are loyal to their brands and they’ve likely deferred their new-car purchases until inventory is available,” said Jessica Caldwell, director of industry analysis at Edmunds.com, a Web site that provides car-buying information to consumers.

Toyota increased incentives by 31 percent from May, though the level remained about $500 a vehicle below the industry average of $2,165, Edmunds.com reported.

Tight supplies of Japanese vehicles have helped push up prices across the industry by giving other carmakers less motivation to offer big discounts. Prices for small cars have risen the most, given the increased demand for fuel efficiency.

The industry’s average transaction price in June rose 2.9 percent from a year ago, to $30,009, topping $30,000 for the first time, according to TrueCar.com.

Analysts said they expected sales to remain somewhat sluggish through much of the summer but pick up later in the year.

“Incentive levels $500 below the first-quarter average and depleted vehicle inventory have added to the pressure as the month progressed,” said Jeff Schuster, the executive director of global forecasting for the research firm J. D. Power Associates. “However, the fundamentals remain in place for a marked return to the recovery pace set in the first four months of the year.”

Some automakers also said sales were hurt on Thursday — the last day of a month often accounts for considerable volume as dealers try to bolster their results — after California enacted a cut in its sales and vehicle taxes, effective Friday. The cuts save the buyer of a $25,000 car more than $350.

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