New York ? At least half a million New Yorkers have diabetes, many of them at risk for blindness, kidney failure, amputations and heart problems because they are doing a poor job of controlling their illness.

The question is, how much privacy are they willing to give up for a chance at better health?

A century after New York became the first American city to track people with infectious diseases as a way to halt epidemics, officials here propose a similar system to monitor people with diabetes, a non-contagious foe.

Conceived after a sharp rise in diabetes deaths over the past 20 years, the plan would require medical labs to report to the city the results of a certain type of diabetes test that indicates how well individual patients are controlling their diabetes.

“There will be some people who will say, ‘What business of the government is it to know that my diabetes is not in control?”‘ said Dr. Thomas R. Frieden, the city’s health commissioner.

The answer, he said, is that diabetes costs an estimated $5 billion a year to treat in New York and was the fourth leading cause of death in the city in 2003, killing 1,891.

By pinpointing problem patients, then intervening ever so slightly in their care, Frieden said the city can improve thousands of lives. “I don’t think we can afford not to do anything,” he said.

The Board of Health vote on the proposal isn’t likely until at least September, but it has already attracted attention from other public health experts and privacy advocates.

The list of illnesses reported to public health authorities has grown over the years, but it still is almost entirely contagious diseases, like HIV, or conditions related to environmental toxins, like lead poisoning.

Diabetes is different, threatening no one but the people who have it.

“This isn’t smallpox,” said James Pyles, an attorney who represents health care groups concerned with medical privacy. “The state, or the city in this case, does not have a compelling interest in the health of an individual that overrides that individual’s right to privacy.”

Pyles praised the intent of the program, but said unless diabetics are asked for their consent, it would be “an outright violation of the constitutional right to privacy” for the government to obtain their identities.

The city’s program wouldn’t initially get consent to collect data, but would allow patients to opt out later. The database would also be tightly controlled, off limits to anyone but department staff, the patients and their doctors, health officials say.

New York’s program would involve collecting the results of A1c tests, which indicate blood glucose control over a few months, unlike the daily glucose tests diabetics give themselves. The A1c test is given for both Type 1 and Type 2 diabetes, the latter linked to obesity and accounting for about 90 percent of American diabetics. The program would cost between $1 million and $2 million a year, the health department said.