BY DAVID OVALLE AND ALFONSO CHARDY

  BONITA SPRINGS - Around here they are known as ''walking ATMs,'' young undocumented Mexican workers with nowhere else to hide wads of cash but in their socks. Every payday, they make easy victims for muggers who know the paychecks won't be in the bank.

  It makes for an uphill battle for Marta Romero, a Mexican-American community activist in this farming town of about 33,000 outside Naples on southern Florida's Gulf Coast. She urges her paisanos -- fellow Mexicans -- to apply for a matricula consular as a way to protect their money.

  A small identification card that resembles a driver's license, the Mexican government-issued matricula has quietly proven successful -- but has created a firestorm of
  controversy in the process.

  That's because the matricula has become a shortcut to legitimacy for undocumented Mexicans in the United States, in effect giving them access to driver's licenses in some states -- though not Florida -- or bank accounts in dozens of financial institutions, including several major ones in Florida.

  The matricula, which the Mexican government has campaigned aggressively to have widely accepted, has infuriated people opposed to illegal immigration.

  ''It's Mexico doing an end run on Congress, trying to bring about a quasi-amnesty for its citizens that the elected representatives of the American people haven't
  supported,'' said Mark Krikorian, executive director of the Center for Immigration Studies, a conservative Washington D.C.-based group.

  CONGRESS SPLIT

  The matricula has sparked acrimonious debate in Congress with federal lawmakers introducing competing bills: one prohibiting the card's acceptance by federal agencies, the other making it as acceptable as a driver's license.

  Bush administration officials have formed a special task force to review the issue.

  The card's popularity has soared since last year when Mexico's 48 consulates began promoting an upgraded version of the matricula.

  More than 700,000 matriculas were issued in 2002, including 14,272 in Miami and 557 in Bonita Springs. More than a million are expected to be issued this year -- less than half the estimated three million to four million undocumented Mexicans nationwide, including about 300,000 in Florida.

  What's even more striking about the matricula is that its success seems to contradict efforts to tighten standards for identification documents for foreign nationals following the Sept. 11 attacks.

  The matricula is now accepted by 75 of the nation's 9,000 banks including Bank of America, Wachovia and Washington Mutual in Florida. It is also accepted as a primary form of identification in about a dozen states to apply for a driver's license.

  The Mexican government has lobbied strenuously to have the card accepted. This week, for example, Mexican officials are meeting with Palm Beach County Sheriff Edward Bieluch to try to persuade his department to accept the matricula as identification for Mexicans in the county, said sheriff's department spokesman Paul Miller.

  OUTREACH EFFORTS

  Many undocumented Mexicans now carry the matricula because Mexican consulates have sent teams out to farming towns like Bonita Springs to sign up people.

  Still, Romero, the Bonita Springs activist, says it's difficult to persuade wary Mexican nationals to sign up for the card.

  ''It's not easy,'' she says. "The immigrants are scared and most don't even know what the matricula offers. Some only speak the Indian languages and most don't even have money to save because they send it all home to their families in Mexico.''

  A key factor in the matricula's success is tacit U.S. endorsement.

  A footnote in an Oct. 21 Treasury report to Congress recommending documents banks could accept to identify foreign account holders said: ``The proposed regulations do not discourage bank acceptance of the matricula consular identity card that is being issued by the Mexican government to immigrants.''

  Betsy Holahan, a Treasury spokeswoman, said it was up to banks to decide what documents to accept.

  It's a profitable business.

  ''People who have these IDs have a large buying power,'' said Tere Hernández, a Washington Mutual spokeswoman. ``We recognize the power of their dollars.''

  Many banks accepting matriculas have made it easier for Mexican nationals to send money to relatives back home. Mexicans remit home between $11 billion and $12 billion a year, according to Bank of Mexico estimates.

  BANKING

  Banks allowing matricula-bearers to open accounts have different rules. Some accept the matricula only for savings accounts -- but others accept it for checking accounts, which enable customers to apply for check and credit cards.

  Immigrant advocates and some bank executives hail the matricula as a milestone in efforts to provide protection for undocumented migrants.

  ''These people are often targeted for robberies because they don't have a place to put their money,'' Hernández said.

  Many anti-immigration advocates accuse Mexico of pushing the matricula as an alternative to the amnesty for undocumented Mexicans that Mexican President Vicente Fox sought -- but failed to win -- in pre-9/11 negotiations with President Bush.

  But Manuel Rodríguez Arriaga, the Mexican consul in Miami, said the matricula was a response to heightened domestic security concerns.

  ''Contrary to what certain groups say, the matricula supports the policy of security because it helps authorities identify quickly and confidently Mexican nationals in the country,'' he said.