SAN FRANCISCO, USA — Google Inc is postponing the market debut of the first computers running on its highly anticipated operating system by about six months to give its engineers more time to fine-tune the software.

Under a new timetable announced Tuesday, Google expects the first machines powered by the operating system to go on sale in the middle of next year. The company previously promised to have its Chrome operating system ready by the end of this year.

Google is recruiting consumers and a handful of businesses to test a “very limited” number of laptops using the operating system, which revolves around the company’s 2-year-old Chrome Web browser. The unbranded computers will be shipped out to people chosen to participate in the pilot program by the end of January.

The first Chrome OS laptops will be made by Acer Inc. and Samsung Electronics Co. Google said the manufacturers will determine the prices of the first Chrome OS machines next year.

The Chrome OS computers will have a 12.1 inch display screen and standard-sized keyboard, but no hard drive. That means the Chrome OS computers will need online access to run more programs. Google is teaming up with Verizon Communications to sell Internet access over Verizon’s wireless network when there is no other way to connect to the Web. The data plans will cost as little as US$9.99 per month and won’t require a long-term commitment.

Google also unveiled a new store for selling applications that run on the Web. That store opened Monday with about 500 applications, hitting the end-of-the-year deadline Google set when it announced the idea in May.