Federal regulators yesterday accelerated a timetable for rules requiring makers of cellular phones to build in features that allow authorities to determine the location of people who dial 911 emergency lines. Cell phones with the feature would begin appearing next year.

"Today's action will hasten the day when victims of car accidents and those stranded in hurricanes can get help sooner," William E. Kennard, chairman of the Federal Communications Commission, said in a statement released after the body's vote. The speedier response by emergency workers "will save lives," he said. Privacy advocates, however, expressed concern that cell phones are being turned into homing beacons.

People often don't know or are too traumatized to say where they are when they call 911. When they use ordinary phones, dispatchers can get the address of the call's originating point using Caller ID. Under yesterday's rule, a 911 call from a cell phone will also be traceable, with accuracy to about 150 feet.

The rule revises an earlier FCC requirement that the phones provide such information, and gives cell-phone manufacturers and phone-service providers greater flexibility in deciding how to achieve the mandated goal.

Under the first version of the rule, passed in 1996, the builders of cellular telephone networks were required to use the signals from nearby cell-phone towers to triangulate and find the caller's approximate position. The revised measure allows an alternative that could be simpler and more precise: building Global Positioning Satellite technology into new phones.

That flexibility cheered representatives of the telecommunications industry. "It was a good day for the FCC," said Thomas Wheeler, head of the Cellular Telecommunications Industry Association.

Nothing in the rules requires that the feature be active at any time other than during 911 calls, and the rules would not prohibit users from turning off the feature for non-911 use. But providing that degree of control over the system could prove challenging to companies.

Despite its obvious public-safety implications, location information is a controversial topic for privacy advocates, who are already upset over another FCC ruling recently that cell-phone companies provide the general location of particular callers to law enforcement authorities who have a court order.

Because the new technologies would allow much closer scrutiny, the burden of proof against violations of privacy should be raised before introduction is allowed, said James X. Dempsey of the Center for Democracy and Technology, a high-tech policy group in Washington.

The beacons should be subject to regulations that will prevent abuse by businesses, he said: "Somebody will dream up a way to use this information for other than 911, that's for sure." For instance, a cell-phone caller trying to find a restaurant might receive directions based on the phone's beacon.

An FCC official who requested anonymity acknowledged that "clearly, there are privacy concerns with the use of this new technology" and expressed hopes that Congress or the commission would act to protect privacy.