By Peter J. Howe, Globe Staff, 4/15/2002

extel Communications, marking its fifth year as the ''official wireless sponsor'' of today's Boston Marathon, is greatly expanding a system that lets the 16,638 registered runners arrange to have automatic updates of their progress in the race sent to friends.

The innovative system uses transponders the size of quarters that runners put on their shoes to send e-mails through Nextel's network. This year, runners will be able to have automatic updates on their progress sent to six e-mail addresses, up from just two last year, says Nextel spokesman John E. Redman. Redman said Nextel hopes to get as many as half the registered runners using the system, up from 22 percent last year.

As runners cross special mats at four of 11 checkpoints on the 26-mile route, readings from the transponders will trigger computer-generated e-mails telling recipients what time they crossed the checkpoint and their estimated arrival time at the finish line in Copley Square.

In another innovation this year, Nextel will provide the wireless access for volunteers carrying Compaq iPaq handheld computers who will be able to look up runners' times as they circulate among spectators. Nextel is also providing 350 of its Motorola phones with walkie-talkie radio service for race organizers, WBZ Radio, and security officials.

Spectators with Net-connected cellphones from Nextel or other carriers also can check runners' standings at www.baa.org/wap.

Peter J. Howe can be reached at [email protected].