Dan Hesse, 46, will take over as president and chief executive officer of Seattle-based TeraBeam Networks Inc, which is developing a novel wireless data technology that uses laser beams for the high-speed transmission of large chunks of data.

Meanwhile AT&T;, the No. 1 U.S. long distance telephone company, is moving quickly to replace Hesse by naming the wireless unit's chief financial officer, Mohan Gyani, as president and chief executive of AT&T; Wireless Services.

In naming Hesse as its new chief, TeraBeam said it expects the 23-year AT&T; veteran to take on the task of building its technology into a force in the market for high-speed telecommunications services.

Privately held TeraBeam, which claims to have been operating in "stealth mode for the past 30 months," makes its official debut on Monday at a tradeshow in Scottsdale, Ariz., the company said in a statement.

Hesse's departure from AT&T; is no surprise. It had been rumored persistently since December, when he was passed over for the top job at AT&T; Wireless Group, parent of the wireless services unit. AT&T; President John Zeglis got that job instead.

Hesse, considered an influential player in the wireless communications business, joins a growing list of top executives to have left Ma Bell in the past two years since C. Michael Armstrong became chairman and chief executive of AT&T;, which is also the top U.S. cable television company.

"AT&T; is losing top talent faster than I can keep track of," industry analyst Jeffrey Kagan, of Kagan Associates, said. "This is obviously a big blow, but not totally unexpected. When the top spot in wireless was given to Zeglis instead of Hesse, many industry watchers knew it was just a matter of time."

Hesse's leaving also comes just weeks before AT&T; is prepared to sell up to 20 percent of its wireless business in a deal that could fetch $8 billion to $10 billion, which would trump the $5.47 billion debut of United Parcel Service Inc. (UPS.N) last November as the largest U.S. IPO ever.

It now falls to Gyani, 48, to fill Hesse's role as head of AT&T;'s domestic wireless voice and data operations, the nation's largest.

"It will be hard to fill Dan's shoes," Kagan said.

Gyani is a recent hire who came to AT&T; from AirTouch Communications, where he had been CFO until Britain's Vodafone bought AirTouch, forming Vodafone AirTouch Plc.

AT&T; said Gyani's will focus will be expanding AT&T;'s wireless footprint nationally, particularly in the data arena.

AT&T; shares were off 5/16 at 52-5/8 in late morning trading Thursday on the New York Stock Exchange.