MTV, the music television giant, plans to launch a US online music store based on technology from Microsoft in a challenge to market leader Apple and its iTunes store, company officials said.

MTV, a unit of media giant Viacom, expects to announce the launch on Wednesday, spokesman Rob Hooper said.

MTV and Microsoft had announced in late 2005 that they were working together on a music service called Urge.

A test, or "beta," version is expected to be available early Wednesday, with more than two million songs available for download.

"We're going to launch a public beta version of Urge in the US tomorrow," the MTV spokesman said. "We have plans to launch it internationally, but we'll make announcements later."

The website www.urge.com displayed a page saying only "Available May 17."

Because of MTV's well-known global brand name and Microsoft's contribution, the service could pose a challenge to Apple and iTunes, which holds the lion's share of the legal online music market.

Published reports said the new service would offer song downloads for 99 cents, following the formula used by iTunes and others, and noted that it may offer a monthly subscription service similar to those of Napster and RealNetworks.

The launch may change the landscape in the so-called format war involving Microsoft and Apple. At present, songs downloaded in the Windows Media Audio (WMA) format cannot be played on iPods, and songs from iTunes cannot be played on WMA devices.

"Urge is Microsoft's and MTV's response to iPod and iTunes," said Jupiter Research analyst Joe Wilcox.

"Microsoft has some pretty good technology with Windows Media Player, but the company has been unable to match the iPod/iTunes experience. Major reason: Microsoft doesn't control all the pieces like Apple does. As a result, the Windows Media experience can and does collapse with respect to iTunes."

Still, Wilcox said that "Microsoft believes that if it can match, or even better, the iPod/iTunes experience, iPod compatibility will no longer matter. The company is betting choice is more important, with respect to devices and music stores. Already, Microsoft has pushed the choice marketing, arguing that with Apple consumers have only one choice."