Patients, please take a number - whether you want one or not.

The government on Monday began hearings on how to assign every American a lifetime health-care ID number - much like a Social Security number - that critics say will demolish privacy by opening medical histories to insurers, employers and others.When President Clinton signed the 1996 Health Insurance Portability and Accountability Act into law, supporters celebrated its guarantee that anyone changing or losing a job would be able to get health insurance, even with a pre-existing medical condition.

But a lesser-known provision of the law contains a requirement for an "identifier" such as a number for each person to streamline the electronic transfer of medical data.

A 17-member advisory panel is still considering what kind of identifier to recommend to the Department of Health and Human Services. It could be a fingerprint or DNA pattern - but testimony suggested a number on an ID card would be most practical.

But before testimony even began, one committee member made clear his dislike for the idea.

"Once everyone's required to use a government-issued health identification card, it may become impossible for any American citizen to walk down the street without being forced to produce that card on demand by a policeman," said Robert M. Gellman, an information policy consultant in Washington.

"You won't be able to use a credit card, cash a check, fly on an airplane, check into a hotel, go to school or enter or leave the United States without showing that card," Gellman said.

Gellman was reminded by fellow panelist Dr. John R. Lumpkin, Illinois' public health director, that Congress has mandated the assignment of identifiers.

Several witnesses testified that not enough legal safeguards exist against misuse of the identifier. Current privacy standards provide for up to $250,000 in fines and 10 years in prison for wrongful disclosure of medical information.

But one witness, Dr. Christopher G. Chute of the Mayo Foundation in Rochester, Minn., said a unique patient identifier - if properly set up - might reduce the dangers of breach of confidence in the present system.

"If fairly and intelligently implemented, electronic patient records using common identifiers might actually reduce risks to patient confidentiality relative to what exists today in our paper environment, which has no ability for audit or usage trail, as it's currently managed," he said.