A study of cellphone use suggests that motorists aren't any better off using a headset in the car than holding the phone to their ear: They're still four times as likely to end up in a crash and injured as are drivers who stay off the phone altogether.

The survey, released yesterday by the Insurance Institute for Highway Safety, said using mobile phones while driving was just as dangerous whether drivers are chatting through a headset or holding on to the handset.

The statistical analysis, which compared phone records with the times of accidents, indicated that the risk was just as great across all age groups and in both sexes.

It's not just keying in phone numbers or calling up messages but the conversation itself that can be the most distracting, said Anne McCartt, the insurance institute's research executive overseeing the study published today in the British Medical Journal.

"There's the possibility that some technology in the future would eliminate distractions from using the phone in the car, but it's hard to think of any way to eliminate the distraction from the conversation," she said. "Your brain can only perform so many tasks at once."

Julie Rochman, an executive with the American Insurance Association, a Washington, D.C., trade group for insurers, said, "This study reinforces the fact that cellphone use is a major distraction and increases injury and death."

The research drew on the experiences of about 500 drivers in Perth, Australia, who were treated in hospital emergency rooms after crashes from April 2002 to July 2004.

Using phone records, McCartt and researchers at the University of Sydney estimated the increased risk of injury by comparing the drivers' cellphone use as much as 10 minutes before their crashes occurred and at control intervals as much as a week earlier.

The institute had to go to Australia to conduct the survey because U.S. phone companies would not permit a look at phone records to verify a driver's distraction at the time of a crash and to allow appropriate comparison periods.

Perth, a city of 1.3 million, bans the use of cellphones while driving unless hands-free devices are used. Still, about a third of the crash victims interviewed had been holding phones to their ears, McCartt said.

The results could bolster the wireless industry's arguments against hands-free laws, or it could have the opposite effect of leading to bans on cellphone use altogether while driving.

"Based on our study, that would make some sense," McCartt said. "But it would be very hard to enforce a law like that."

The institute, a nonprofit research group funded by U.S. insurers, has not taken a position on any legislation. A hands-free law, however, could at least help encourage drivers holding their cellphones to their ears to put them down, preventing some accidents, McCartt said.

Cellphone customers spend more time talking on their phones while in their cars than anywhere else. Last year, they spent 40 percent of their time on mobile phones while driving, compared with 24 percent while in the home, according to an April survey of consumer habits by the Yankee Group, a research firm in Boston.

Several states have banned the use of handheld cellphones while driving.