DETROIT (Reuters) -- U.S. sales fell for all three big American automakers in June, led by a 26 percent drop at General Motors, while Japan's Toyota Motor Corp. surged.

Higher gas prices, slower sales of trucks and sport utility vehicles and a lack of deep incentives compared to last summer -- when GM rolled out employee-level pricing -- hurt the Detroit-based automakers in a mostly slack U.S. auto market.

The tough sales comparison comes at a time when GM's board is under pressure to consider a three-way alliance with Renault SA and Nissan Motor Co.

Ford's June sales dropped 7.1 percent and DaimlerChrysler's plunged 13.2 percent, underscoring the pressure on Detroit automakers at the start of the summer season when they will need to clear out their unsold inventory of 2006 models.

By contrast, Toyota -- now No. 3 in the U.S. market -- posted a 14.4 percent gain.

Toyota has taken a bigger share of a weakening U.S. market on the fuel efficiency of its line-up, which trails only Honda Motor Co. in average fuel economy among major manufacturers.

In the first half of 2006, Toyota sales rose 10 percent, boosted by the revamped Camry sedan and the new Yaris subcompact. "We expect that sales pace is going to continue in the rest of the year," said Jim Lentz, executive vice president of Toyota Motor Sales.

He said Yaris sales were stronger than anticipated and Toyota was working to import them in higher volume from Japan.

Toyota has only a 9-day inventory of the Yaris, and an even tighter 4-day sales inventory of its Prius hybrid, essentially making both vehicles sellout hits.

Meanwhile, sales of Ford's Explorer, a best-selling SUV, dropped by 36 percent in June while sales of the larger Expedition were down 46 percent. "There's no question that higher gas prices have hurt demand for these products," said Ford sales analyst George Pipas.

Auto executives said there were signs that consumers were also waiting for better deals in July, when both GM and Chrysler rolled out new discount offers.

CHRYSLER INCENTIVES UP, SALES DOWN

The weak June numbers capped a rough quarter for Chrysler, the only Detroit-based automaker to post a profit in the first quarter. Chrysler, sitting on an unsold inventory of over two months of vehicles as of the end of May, has had to resort to the biggest discounts in the industry this year.

DaimlerChrysler's first-half U.S. sales were down 5 percent as a 17 percent gain for Mercedes-Benz was more than offset by a 3 percent drop for the bigger-volume Chrysler brand.

Over the weekend, Chrysler attempted to shore up its flagging sales with the most aggressive discount offer of the year, combining employee-level pricing with zero-percent financing and a 30-day money back guarantee.

GM said its June sales result, in line with the company's cautionary forecast, was on track with the terms of its restructuring plan, which includes a dozen plant closings and some 30,000 job cuts.

The year-on-year GM decline reflected comparison to an unusually strong performance in 2005 when it rolled out an employee pricing offer that touched off a summer price war in Detroit.

GM has vowed to avoid cutting margins through a similar sweeping incentive program this year. It offered a more limited zero-percent financing deal over the weekend, but executives have said such sweeping discount programs hurt its brands last year, as well as the resale value of its vehicles.

GLOBAL POWERHOUSE?

Billionaire investor Kirk Kerkorian is looking to broker the three-way alliance among GM and Nissan-Renault. Such a tie-up would create a global automotive powerhouse with almost twice the sales of Toyota, the No. 2 automaker worldwide.

The boards of Nissan and Renault on Monday approved discussions about the deal. Nissan Chief Executive Carlos Ghosn, who is credited with spearheading that company's revival, also heads Renault, which has a controlling stake in Nissan.

But Nissan has struggled in the U.S market this year, and its June sales tumbled by 19 percent.

Nissan's difficulties have included a disruptive move in its headquarters to Nashville, Tennessee, production cuts and an embarrassing recall of some Altima and Sentra sedans due to evidence of engine fires.

Rival Honda Motor Co., which is building a new U.S. assembly plant to keep up with demand, posted flat overall sales in June. Strong sales for its fuel-efficient Fit and Civic models were offset by declines in truck sales and for its Acura luxury line.

Among other automakers:


Hyundai Motor America and Kia Motors America sales climbed a modest 2.6 percent to 71,951.


Volkswagen of America sales in the U.S. increased 7.3 percent to 28,430.


BMW of North America sales increased 2.7 percent to 27,763.


Mazda North America sales rose 7.5 percent for the month to 23,727.


Mitsubishi Motors North America sales fell 5.8 percent to 10,004.


Porsche Cars North America sales grew 12.5 percent to 2,871.


American Suzuki Motor sales spiked 27.7 percent to 9,516.


Subaru of America sales rose 3 percent to 18,476.


Isuzu Motors America sales fell 42.2 percent to 745.