DETROIT — Buick has landed a spot at the top of the influential J.D. Power Vehicle Dependability Study, tying with Lexus. It was the first time in more than a dozen years that any brand other than Lexus had been at the top of the study.

General Motors, which owns Buick, has been aiming for quality improvements as a way to win back customers who fled domestic car brands for imports. The company's July market share was 23.9 percent in the United States, its most important market, down from 27 percent just a year ago. That makes winning new customers a more critical goal than ever before.

Three GM brands were ranked in the top 10 on the dependability study — along with Buick were Cadillac and the now-defunct Oldsmobile.

The Vehicle Dependability Study looks at problems reported over three years. So this year's study, released yesterday, looked at 2004 model year cars.

"It's big news for GM to be on par with Lexus," said Katherine Benoit, executive director of Pontiac-Buick-GMC. "I think it signifies that we have, indeed, made a lot of progress, and we are closing the gap on quality."

Benoit said the company will soon begin touting the J.D. Power award in advertising.

Studies show long-term dependability is one of the top concerns for customers shopping for new cars, along with monthly payments, safety and styling.

Lexus, which saw its score drop slightly due to the introduction of two new brands in 2004, will continue to focus on quality, parent company Toyota says. New or redesigned models tend to have more problems before kinks are worked out.

"Internal studies show that dependability is consistently the top purchase reason for Toyota, Lexus and Scion buyers, and we will continue to prioritize quality as our product offerings and sales volume increase," said Jim Lentz, Toyota Motor Sales executive vice president.

The J.D. Power survey asked 53,000 original owners of 2004 model-year cars to rank their vehicles on 147 different problems in nine different categories.

About 65 percent of owners needed to replace a part during the first three years. Neal Oddes, director of product research and analysis for J.D. Power, said some issues were less problematic to buyers than others. If an engine needed to be replaced early on, it could ruin the car owner's experience. But replacing small or inexpensive parts weren't a big deal, provided the car didn't need too many repairs.

The brands at the top of the list were both domestic and foreign, mass market and luxury.

"People don't have to necessarily spend premium money to get equal value," Oddes said. "That's good news for people."