* Telefonica, America Movil and competitors sign up

* Spectrum auctions meant to boost competition

* Televisa teams up with Nextel Mexico (Recasts, adds background, byline)

MEXICO CITY, Feb 18 - Tycoon Carlos Slim's America Movil (AMXL.MX) and Spain's Telefonica (TEF.MC) are among 17 companies that have signed up to bid for wireless spectrum being auctioned in Mexico later this year.

Other smaller telephone and cable companies have registered too for the auction, according to information released on telecommunications regulator Cofetel's website www.cofetel.gob.mx late on Wednesday.

The auctions are at the center of a government push to stoke lackluster competition in an industry long dominated by Slim. America Movil is the leading wireless operator in Mexico, with Telefonica a distant second.

After years of delay, the auction of spectrum in the 1.7 GHz and 1.9 GHz bands is key to operators that want to expand their services and offer increasingly sophisticated products like wireless video and Internet.

Telefonica lacks third-generation frequencies in central Mexico, which means clients who use smartphones have limited access to some services in Mexico's capital, a key market.

A partnership between giant media company Televisa(TLVACPO.MX) and the Mexican unit of NII Holdings Inc (NIHD.O) and other companies controlled by businessman Ricardo Salinas Pliego, including broadcaster TV Azteca (TVAZTCACPO.MX), have also signed up for the auction.

Televisa unveiled a deal this week to buy 30 percent of NII Holdings' Nextel Mexico for $1.44 billion.

The money Televisa is paying for the share in Nextel Mexico would be used by Mexico's No. 4 wireless operator to bid for spectrum and to overhaul its network infrastructure.

Cable operator Megacable (MEGACPO.MX) has also signed up for the auction.

Slim's America Movil (AMX.N) controls more than 70 percent of the mobile telephone market in Mexico, where it operates under the Telcel brand. (Reporting by Michael O'Boyle, editing by Gerald E. McCormick)