For the second time in less than two years, hormone replacement therapy has failed to live up to its billing as a preventive for heart disease in older women, causing federal health officials to halt a clinical trial involving 11,000 women.

Officials yesterday said they stopped the trial of estrogen replacement therapy in postmenopausal women early because it didn't provide the hoped-for reduction in heart disease risk, but did slightly increase the risk of stroke.

Participants in the estrogen-only arm of the Women's Health Initiative were instructed to stop taking their study drugs, said Dr. Barbara Alving, leader of the study and acting director of the National Heart, Lung and Blood Institute.

About 300 of the women in the estrogen trial were enrolled in the study through the University of Pittsburgh.

Although there's no emergency, "we've stopped this study in the interests of participant safety," Alving said. "These findings reinforce previous recommendations that women should not take hormone therapy to prevent heart disease."

However, she added, hormone replacement is still indicated for women who have menopause symptoms such as hot flashes and for those at high risk of osteoporosis but who cannot take non-estrogen drugs.

The U.S. Food and Drug Administation and the NIH advise using the lowest possible doses for the shortest time periods.

In July 2002, the NIH called a halt to another arm of the Women's Health Initiative that tested a combination of estrogen and progestin.

Along with an increased risk of breast cancer and heart attack, that group had eight more strokes for every 10,000 women per year.

A similar stroke risk was found among women who took estrogen alone, said Dr. Jacques Rossouw, a project officer for the study.

"If you don't have a benefit for heart disease, this increased risk for stroke becomes an important consideration as to whether we should continue this trial or not," he noted.

The WHI was devised to assess whether hormone replacement therapy reduced the risk of cardiovascular disease, as the medical community had long believed.

All of the women were 50 to 79 years old, were postmenopausal and had had hysterectomies. They were randomly assigned to receive either estrogen or a placebo.

After almost seven years of follow-up, the researchers found that estrogen treatment reduced the incidence of hip fractures. But it didn't increase the chances of developing breast cancer, a surprising finding that Alving said would prompt much discussion and speculation in the scientific community.

Alving said detailed results won't be available until the research is published in a medical journal, probably in April.

Dr. Lewis Kuller, leader of the Pitt study site, said that women who need to be on hormone therapy should minimize their risk for heart disease and stroke by maintaining a healthy weight with diet and exercise, and with smoking cessation and control of blood pressure, blood sugar and lipid levels.

The studies do not shed light on the short-term benefits and risks of hormone replacement among those women taking it to relieve menopause symptoms.

"If you're symptomatic, you don't have to stop the medication," said Dr. Richard Guido, a gynecologist at Magee Womens Hospital.

"You just have to be well-informed about the risks of taking it."

After the earlier trial was halted in 2002, the proportion of women over 50 using any hormone replacement therapy dropped from about 40 percent to 28 percent. Guido expects that number will drop further in light of the new findings.

For more information, go to www.nhlbi.nih.gov/whi.