At the Miller household, they switched to bottled water the other day, the morning after Lori Miller learned by chance what Anne Arundel County has known for months but never told her family directly, nor thousands of others: Potentially harmful levels of radium have been detected in an increasing number of the 12,000 private wells in the county's northern half.

Why, Miller wondered, had there been no official letter about the possible danger in the well that lies 15 feet out the back door of the family's farmhouse on five acres in Millersville?

"My head was ready to blow off," said Miller, whose two daughters--ages 2 and 3--have been nourished on formula mixed with water from the well. "Basically, they weren't going to bother notifying the homeowners."

County officials say that, in fact, they have publicized the risk widely, using community meetings, the media, a Web site and fliers sent home with schoolchildren to urge users of every well to have it tested and, if necessary, to install a water softener, which eliminates nearly 100 percent of radium.

Another community meeting is scheduled for Wednesday at Arundel High School.

But to date, no notice of possible contamination of wells has been sent to the homes that might be affected. As a result, many residents, like Miller, have learned only recently about the radium problem, first discovered in a handful of wells in 1998 and many more since then.

"They are irate," said Donald Yeskey, president of the General's Highway Council of Civic Associations, which represents 15,000 households, most of them dependent on wells. If not for a November article in an Annapolis newspaper, "we'd still be in ignorant bliss," said Bob Grimm, president of the 100-member Indian Landing Community Association.

An official familiar with the radium problem, who asked not to be identified, agreed that instead of hoping residents attend meetings or read articles, the county should have reached out with a letter to each home, calling it a "good and inexpensive public-policy thing to do."

Radium, a metal that occurs naturally in ground water under certain geologic conditions, can cause bone cancer, but only if drunk for decades at above-standard levels, officials said.

Given the average dose found in tainted wells in Anne Arundel County, a resident whose home does not have a water softener would receive about as much radiation in a year as a chest X-ray provides.

Health records show no unusual number of bone cancer cases in the county, the officials added, and they have not urged residents to stop drinking well water.

"The levels they've found are not the kind where you glow in the dark," said Mike Burke, a regional official of the federal Environmental Protection Agency. "It's not [a problem] you need to hit the panic button about. It's one people need to pay attention to and deal with."

"There is a risk there," said Bob Weber, director of the county Division of Community and Environmental Health, "and in our opinion, if you can minimize your risk . . . you should do so."

Because Anne Arundel has a high general rate of cancer, officials decided in 1996 to run tests on 50 of the 40,000 wells in the county, which digs more wells annually than other counties in Maryland, in part because its geology makes tapping ground water relatively easy.

Although the tests did not find explanations for the county's overall cancer rate, they did find levels of radium higher than EPA standards in 15 of the 50 wells tested.

That prompted county officials to order a radium test on any new well dug.

Since June 1998, above-standard levels have been detected in 63 percent of 600 new wells, with the average tainted well having three times EPA recommendations for radium. And samples taken from 101 older wells found high levels in half of them.

"If someone has a well in the affected area, it's certainly a significant possibility that they have elevated levels," said Tom Gruver, supervisor of the well construction and water quality program of the county Department of Health.

As the scope of the problem has become known, county officials said, news releases and meetings seemed the most effective way to alert residents. Perhaps tempering any sense of urgency, at least 70 percent of residents who use wells "already have some sort of water conditioner" for reasons unrelated to radium, Gruver said.

Beyond that, notifying residents directly would have been difficult, officials said, because the county does not have a database of wells.

It has no statutory responsibility for maintaining or regularly inspecting wells. Yeskey, however, said finding well users would be easy: From property tax rolls, subtract any homeowner who is billed for water by public or private providers.

Miller, an environmental engineer, learned of the problem because a neighbor asked her to attend a Jan. 11 meeting about tainted wells to decipher technical details for him. She assumed any problem was small because she had heard nothing about one.

But as officials outlined the issue, "I was just so upset," Miller said. Not only did her family switch to bottled water, she took samples of her well water to associates for testing. Preliminary results suggested her household filtering system already eliminates radium, which was "a huge relief to me."

But with thousands of homes potentially affected, Miller said, the county should notify each owner personally. Miller said she wants "a letter in my mailbox that says, "Dear Homeowner: You live in this area. There's a potential for radium.' "

On Friday, Weber said the county was considering sending just such a letter.