Toyota Motor will extend the time it takes to develop its vehicles by an

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average of four weeks in an effort to ensure quality after a string of high-profile recalls, a top executive said Wednesday,

‘‘The fast growth of the past decade has been too much in some areas for the company to keep up with,’’ the executive, Takeshi Uchiyamada, executive vice president, told a small group of reporters based in the United States who were visiting Toyota’s headquarters,

Mr. Uchiyamada, who is in charge of research and development, said Toyota had assigned about 1,000 engineers from the 14,000-member research and development staff to deal with quality issues,

The quality of Toyota’s cars, once a benchmark for the industry, has come under scrutiny since the company, the world’s top automaker, recalled more than 10 million vehicles globally, starting late last year, mostly for problems with unintended acceleration,

Criticized by regulators for being too slow to act and out of touch with consumers’ needs, Toyota has also set up a new team of 100 engineers independent of development to audit vehicle quality from the perspective of drivers, Mr,

Uchiyamada said,

‘‘It’s important for our engineers to look at a vehicle and see how customers might use it in ways that haven’t been reflected in our testing,’’ he said, adding that doing so could help identify problems like stacked or loose floor mats — one of the factors cited in unintended accelerations — before they hit the market,

‘‘We want them to be a little mean.’’ Toyota announced a number of steps earlier this year to reverse a quality slide and win back consumer confidence, including formation of a 50-member committee, headed by the company’s president, Akio Toyoda, aimed at giving more autonomy to regional operations to speed up decisions on quality issues,

The various initiatives to improve vehicle quality are likely to result in a slight rise in development costs per vehicle in the short term, Mr. Uchiyamada said. The average lead time for vehicle development in Japan has so far been about 24 months, he said,

‘‘Our personnel costs are fixed. We’re not hiring new engineers, so over the long term, if our quality stabilizes, I expect our costs should fall,’’ he said,

Mr. Uchiyamada said Toyota had added a new layer of management in engineering, appointing assistant managers to create smaller work teams and focus more on developing skills among workers and driving home the ‘‘Customer First’’ philosophy,

Still, in a sign that such efforts could take time to bear fruit, recalls have not let up at Toyota. This week, Toyota recalled 270,000 cars.