AT&T Inc. opposes a quick federal approval of the proposed wireless-spectrum merger between its competitors Sprint Nextel Corp. and Clearwire Corp. that would create a national WiMAX network.

Comcast Corp., Time Warner Cable Inc., Google Inc. and Intel Corp. are major investors in the WiMAX venture for superfast wireless Internet and video.

AT&T spokesman Michael Balmoris said today: "We're not against WiMAX or those particular parties." But he said Sprint and Clearwire had said different things about the amount of wireless spectrum to be used in the WiMAX venture, valued at $12 billion.

AT&T has asked the Federal Communications Commission to mount a full competitive market review, Balmoris said. AT&T separately has said it could launch its own WiMAX system for rural areas.

Scott Sloat, spokesman for Sprint, said the new venture had "exhaustively documented all our spectrum holdings. AT&T seems to be a little upset that someone should have more [wireless] spectrum than AT&T."

WiMAX will bring competition to the wireless industry, Sloat said, and Sprint still expects the merger to close in the fourth quarter.

In May, several companies announced the WiMAX venture, with Comcast saying it would invest slightly more than $1 billion. Other investors are putting in an additional $2.2 billion, for a total financial investment of $3.2 billion. The venture is central to Comcast's current wireless strategy.

Clearwire, founded by wireless mogul Craig O. McCaw, is based in Kirkland, Wash.

As the FCC considers the deal, Sprint will introduce WiMAX in Baltimore next month, its first big market, and then Washington, Sloat said. The details on cost for the service have not been released. The service will be offered to businesses and consumers in Baltimore through Sprint's Xohm business unit. Sprint will fold Xohm into Clearwire for the new WiMAX venture.

The WiMAX service could be introduced in Philadelphia in 2009, Sloat said. WiMAX wireless Internet speeds would be similar to those available with a cable modem, companies have said.

The investment by Comcast, Google and others will finance marketing and development to take the WiMAX venture national.