DES MOINES, Iowa -- Two mammograms within 10 months in 1994 cleared Lorna Johns of breast cancer so she decided to skip the X-ray the following year.

"That was wrong," she said. "That was the one I shouldn't have skipped."

She was 68 when her doctor discovered a lump during a 1996 exam. A lumpectomy soon followed, then radiation therapy to help rid Johns of one of the most commonly diagnosed cancers in women.

Six years after Medicare began paying for an annual mammogram for women over 40, only 51.8 percent of the eligible women over 50 had at least one mammogram in 2001 or 2002, according to the federal Centers for Medicare and Medicaid Services. That translates to about 7.6 million women nationwide.

The numbers suggest older women may be misjudging the value of regular breast cancer screenings.

"There's a perception, that's probably wrong, that breast cancer is a disease of young women. It's not, it's a disease of older women," said Dr. Stephen Taplin of the National Cancer Institute.

Thirty million mammograms are done each year in the United States. The breast X-ray has long been considered the best way to detect breast cancer, which strikes about 200,000 women a year and kills 40,000 of them.

In recent years scientists themselves may have sown doubt among women about whether an annual mammogram is any better than getting one every other year.

Taplin, however, said no study has compared the two intervals, and there is insufficient evidence to support annual over biennial mammography. "Every one or two years is not the issue. Women who are not being screened at all are the ones who are at risk of having poor outcomes," he said.

Mammography rates for Medicare-eligible women over 50 are inching up at a snail's pace, and in some states not moving at all, according to the Centers for Medicare and Medicaid Services, which run the Medicare and Medicaid programs.

Figures from the Iowa Foundation for Medical Care, which tracks Medicare claims in the state, show 52.7 percent of Medicare eligible women over 50 had a mammogram in 2001 or 2002. That rate has remained stagnant for the past five years.

Johns was part of a women's health study at the University of Iowa in 1994 and had two mammograms -- one by the university, the other ordered by her doctor.

"I had two in a short time and I thought, 'I won't have one this year,"' she said.

Luckily, the cancer was found before it spread and became life-threatening. But the diagnosis meant that for five years after surgery she was on the drug tamoxifen, which slows or stops the growth of new breast cancer cells. She has remained cancer-free.

For 75-year-old Betty Grandquist, of Des Moines, a routine mammogram in 2002 found breast cancer.

"By getting it that early, it was not in the lymph nodes, so they could do a lumpectomy," she said.

The American Cancer Society recommends a yearly mammogram for women starting at age 40.

On average, mammograms find about 75 percent of cancers, said Debbie Saslow, the society's director of breast and gynecological cancer. Five-year survival rates for early detection, before the cancer spreads to the lymph nodes, are between 96 percent and 97 percent, she said.

Most breast cancer risk is tied to a woman's lifetime exposure to estrogen, Saslow said.

"The older you get, the more, of course, you've had," she said. "But after menopause, things change a lot and post-menopausal breast cancer is much more common than pre-menopausal breast cancer."

In Florida, from April 2001 to March 2003, 64 percent of Medicare-eligible women aged 50 to 67 received a mammogram, a rate unchanged since 1999.

"The numbers are not great, but the fact that we can't move those numbers, that's what has us worried and trying to figure out what we need to do," said Bonnie Mason of Florida Medical Quality Assurance in Tampa, which examines Medicare claims.

Mason said the group has worked with doctors, distributed mailings and articles, and held outreach programs, health fairs and exhibits at conferences.

"Aside from bribery, I don't know what we need to do," she said.

Health officials in New Mexico might have found an answer.

The New Mexico Medical Review Association combined an aggressive media campaign targeting older women with one involving doctors and radiologists, along with reminder phone calls.

One tool doctors use is a string of beads to help patients visualize the size of lumps. The smallest bead, about the size of a baby pea, represents a lump that can be detected by regular self-exams, a mammogram and a doctor's exam; the largest, at 1.5 inches in diameter, or about the size of a golf ball, is the size that a woman might discover by chance.

The success of the campaigns has driven up the state's mammography rates among women aged 52 to 69 in the last three years -- from 55.7 percent to 60 percent.

The Iowa foundation plans to work with about 2,000 physicians to encourage their patients to get a mammogram.

Grandquist understands women's fear of learning the worst, especially women her age.

"If someone had breast cancer, it was a death sentence. So they don't want to deal with it," she said. "You have to get over the fear factor. It's how early you get it, the better chances of survival."

Johns, who doesn't skip her annual mammograms any more, has launched her own campaign about the importance of regular screenings.

"I feel good. And my friends have all had their mammograms," she said.