Dr. Ronald Herberman urged a U.S. House subcommittee yesterday to support more research into the potential health effects of cell phone use and urged precautions in using the devices, particularly by children.

Dr. Herberman, director of the University of Pittsburgh Cancer Institute and UPMC Cancer Centers, acknowledged that definitive evidence is lacking that cell phone use is harmful. But his calls for caution caught the attention of members of the Subcommittee on Domestic Policy, particularly when he produced a three-dimensional model that estimated the greater penetration of electromagnetic fields from cell phones into the brains of children compared to adults.

Children have thinner skulls, he said, and protective myelin sheaths for nerves in the brain are less developed.

The model prompted Rep. Dennis Kucinich, D-Ohio, the subcommittee's chairman, to beckon for it as he asked follow-up questions.

Dr. Herberman made worldwide news in July, when he apparently became the first U.S. cancer center director to issue an advisory to staff and faculty about the potential health risks of cell phone use.

In his opening statement, Mr. Kucinich referred to that advisory without naming Dr. Herberman directly, saying a pre-eminent cancer specialist helped bring public attention to the debate among scientists about whether long-term cell phone use causes tumors.

Both sides of the debate were represented at yesterday's hearing, though a representative of CTIA-The Wireless Association, an industry group, declined to testify.

Dr. Robert Hoover, director of epidemiology and biostatistics for the National Cancer Institute, cited studies that he said found "no convincing evidence" linking cell phone use with brain tumors. On its Web site, the institute says a "growing body of research" does not support suggestions that cell phone use may increase the risk for brain cancer.

Dr. Herberman objected that Dr. Hoover's remarks and a list of references on the National Cancer Institute Web site do not mention studies by a Swedish researcher that suggest increased cancer risk among long-term cell phone users.

In his testimony, Dr. David Carpenter, director of the Institute for Health and Environment at the University at Albany, State University of New York, urged prompt action.

"This is a critical public health issue," he said, adding that some recent studies have suggested that cell phone use early in life greatly increases the risk for developing cancer. He urged federal agencies to issue warnings, particularly for children.

Ellen Marks of Lafayette, Calif., told the subcommittee that she believed heavy cell phone use over 20 years by her husband, Alan, contributed to his brain cancer.

Before it was diagnosed earlier this year, he had long had personality changes, apparently linked to the cancer, that severely affected his family, Mrs. Marks said.

She said she testified "in an effort to help others escape our fate."

Dr. Herberman told the committee that some research suggests that people who use cell phones the most have double the chance of developing malignant brain tumors and tumors on the hearing nerve, known as acoustic neuromas.

Based on current evidence, "I cannot tell this committee that cell phones are definitely dangerous," he said. "But I certainly cannot tell you that they are safe." He urged precautions, like limiting use among children and using an earpiece or speaker option to keep the phone away from the body, until more definitive research is available.

Dr. Herberman also asked the committee to persuade the cell phone industry to cooperate in independent studies. Mr. Kucinich said the subcommittee would "continue to seek the cooperation of the industry about the information that has been presented."

The ranking Republican on the subcommittee, Rep. Darrell Issa, R-Calif., said Americans deserve to know more about device emissions.

"On both sides of the aisle, there was a recognition that people need to pay attention to this problem," said Dr. Louis Slesin, editor of Microwave News, which tracks research related to the issue. He noted that yesterday's congressional hearing was the first in 15 years on cell phone safety.

Dr. Herberman's oral and written subcommittee testimony is available at www.environmentaloncology.org. Other subcommittee testimony and a video of the hearing are available at domesticpolicy.oversight.house.gov.