The newest drug to fight osteoporosis now has been shown to reduce by half the risk of broken hips.

The Food and Drug Administration in October approved alendronate to fight spinal fractures. But nobody knew then that it also reduced the bigger threat of a broken hip.

Alendronate, whose brand name is Fosamax, is the first nonhormonal treatment for the bone-weakening osteoporosis that strikes about 25 million Americans, the vast majority of whom are aging women.

It has been proven to fight spinal fractures, the small breaks that cause the humped back characteristic of osteoporosis. But its effects on broken hips may be more significant. Some 20 percent of women who break a hip die within a year, and many wind up in nursing homes.

The new study, funded by Merck but conducted by the University of California, San Francisco, suggests alendronate prevents hip fractures as effectively as the controversial hormone estrogen does.

Some 2,000 high-risk osteoporosis patients took either alendronate or a dummy pill every day for almost three years. The alendronate patients had a 51 percent lower risk of hip fracture, said UCSF biostatistician Dennis Black, who will present his study today at the World Congress on Osteoporosis in the Netherlands.

Other studies have shown estrogen halves the hip fracture risk too, said Dr. Ethel Siris of the Columbia-Presbyterian Medical Center in New York. While estrogen also prevents heart disease, many women still agonize over taking it because of various side effects, and Siris predicted the alendronate study could help some make their choice.

``If you're scared of estrogen or can't take it, this is a drug that appears to do the same thing,'' she said. ``That's a big added advantage for alendronate, and it's very good news for women.''