LOS ANGELES — Two new reports are pointing to a rapidly changing auto world where American and South Korean brands are equaling the quality of the top manufacturers and making large gains in market share.

The data show that Ford Motor Co. is beginning to solidify its position as the top auto seller nationally and it, along with the Buick division of General Motors Co., are edging out luxury brands such as Lexus and Mercedes-Benz in the latest quality rankings.

Ford’s Lincoln brand trailed only Porsche in the J.D. Power and Associates 2010 Vehicle Dependability Study released Thursday.

Lincoln owners reported problems at a rate of 114 per 100 vehicles during the first three years of ownership, slightly higher than the 110 rate reported by Porsche owners. Buick and Toyota Motor Corp.’s Lexus brand tied for third.

All three Ford brands — Lincoln, Ford and Mercury — outperformed the industry. While GM’s Buick and Cadillac lines also scored better than average, its Chevrolet division was worse than average. Chrysler Group’s Jeep brand, Volkswagen, Suzuki and Land Rover scored the poorest, logging problems at double the rates of the top makes.

Steady quality improvements are one reason Ford has logged huge gains in market share over the last year, according to a study of March car sales by TrueCar.com, an auto information company. During the first half of March, Ford was the leading auto seller in the United States, with 19.2 percent of the market. That’s up from 14.6 percent during the same period last year.

Other domestic brands are making gains.

Buick’s improved quality image is allowing an aging brand to start to make sales gains. Its market share rose above 1 percent in early March, TrueCar said.

In its study, J.D. Power collected 52,000 responses from owners, asking them about their experiences with their vehicles. The surveys were conducted in late 2009, which for the most part was before recent large recalls by Toyota and American Honda Motor Co.

The dependability report found that seven of 10 models with the lowest incidence of problems are from Ford and GM, including the 2007 Buick LaCrosse, Buick Lucerne, Cadillac DTS, Ford Five Hundred, Lincoln MKZ, Mercury Milan and Mercury Montego.

Overall, the industry continues to make steady quality improvements, with 25 of the 36 vehicle brands increasing long-term dependability ratings in 2010 over 2009.

On average, owners experience just 155 problems per 100 vehicles during the first three years of ownership. That’s a drop from 167 a year ago.

Hyundai, also rising in J.D. Power’s rankings, has surpassed Nissan and held 9 percent of the auto market in early March, up from 7.6 percent, TrueCar said.

“Hyundai has increased in quality over the last several years. It is another one of those brands where its quality perception is just starting to catch up with its true quality,” said J.D. Power analyst Steve Witten.

The Korean automaker has an aggressive discounting strategy and has positioned itself “as a value brand, and that’s what consumers want to hear right now and they match up well against Toyotas and Hondas,” said Jesse Toprak, a TrueCar analyst.

GM, now the No. 2 auto seller, is holding steady with a 17.8 percent market share.

Toyota, which had seen a large drop last month, is back up to 15.5 percent of the market, the same it held at this time last year.

Aggressive sales and financing incentives and lease deals helped it regain sales lost to its recalls and image problems, Toprak said.

He estimates that Toyota incentives rose from $1,800 per vehicle in February to $2,550 in March. That compares with $1,600 in March 2009.

Honda, possibly hurt the most by Toyota’s sales strategy, has seen its share drop this month almost a full percentage point to 9.4 percent, Toprak said.

Chrysler Group continues to give ground, falling to 9.9 percent of the market from 11.8 percent a year ago.