Federal regulators as early as today are expected to take a major step toward development of a nationwide emergency alert system that would send text messages to cell phones and other mobile devices wherever a crisis occurs.

Lack of a simple way to deliver vital warnings to residents has hindered emergency response in disasters such as Hurricane Katrina, recent college-campus shootings, and a spate of devastating tornadoes in the Southeast in February.

The Federal Communications Commission is slated to establish technical standards and other requirements that for the first time would make such communication possible, two FCC officials say. The officials requested anonymity because commissioners have not yet voted on the plan.

Although wireless carriers would not be required to upgrade their networks to accommodate the alerts, those that agree to participate would have to implement the FCC's standards.

All four national cell-phone providers — AT&T, Verizon, Sprint Nextel and T-Mobile — said they almost certainly will take part if the FCC adopts an advisory committee's recommendations on how the system would work. The agency is expected to approve those proposals, which, among other things, would initially limit warnings to the English language and 90 characters in length, officials say.

The network is expected to be up and running by 2010.

Under the planned system, a county, state or federal first responder would send an alert to a still-to-be-determined federal agency that would serve as a clearinghouse. That agency then would relay the alert to participating wireless carriers.

The system could be used for a variety of incidents, such as severe weather, a terrorist threat or child abduction. A message could be sent to a county, region, state or the entire nation.