WASHINGTON — Detailed new research shows that using a cell phone behind the wheel is a key cause of traffic accidents and that hand-free devices provide little safety benefit, federal officials told an international automotive safety gathering Wednesday.

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But whether drivers use a hand-held device or not, “phone use degraded both driving performance and vehicle control,” said NHTSA’s Elizabeth Mazzae.

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NHTSA officials have expressed concern that hands-free devices can give drivers a false sense of security, when research has shown that it is the act of conversation that leads to distraction and inattentive driver behavior.

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The federal research presented Wednesday adds to a growing body of studies that suggest hands-free cell-phone systems will not deliver the safety benefits automakers and legislators hoped for.

In 2003, for example, University of Utah professor David Strayer found cell-phone conversations can lead to a kind of “inattention blindness,” as drivers fail to recognize objects or events in their field of view. Strayer found that drivers using hand-held and hands-free cell phones were equally impaired.

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Greg Rosinski is a Canton, Mich., resident who uses his cell’s speaker phone function. He said studies about the dangers of cell phone use while driving tend to exaggerate.

“Having a baby or even another person in the car is just as distracting,” said Rosinski, a former account representative for a cell phone company. “I don’t buy any of this scare tactics stuff. Cell phones are no more a cause of accidents than someone applying mascara or eating in the car.”