Motorola has notified customers of Iridium, the financially troubled satellite telephone system it bankrolled, that service would end March 17 unless a buyer for Iridium comes forward.

In a letter sent last week to customers who bought Iridium phones directly from Motorola, the Schaumburg, Ill.-based telecommunications company said it would continue support for Iridium until March 17, when Iridium_s last-ditch financing runs out. Motorola was the primary backer of Iridium and owns a stake in the company, which filed for Chapter 11 bankruptcy protection last August. "Unless a qualified buyer comes forward and provides additional funding by March 15, 2000, we do not expect Iridium service to be available after 11:59 p.m. EST on March 17, 2000," Motorola_s cellular service division said in the letter dated March 6. If Iridium does not find a buyer in time, it will dismantle the satellite system, leaving Iridium subscribers with useless phones. Motorola said the phones would not work with other satellite telephone systems. Iridium, which allows customers to make phone calls from anywhere in the world via a network of orbiting satellites, struggled to sign up subscribers to its pricey service. Critics said the phones, which cost as much as $3,000, were too bulky and required a separate antenna for use indoors or in cars.