The government approved a hormone-blocking drug Monday to help extend the lives of men suffering from prostate cancer - the third leading cause of cancer deaths among American males.

The Food and Drug Administration gave doctors the go-ahead to use the drug, called flutamide, in combination with leuprolide, a previously approved drug that affects hormone production in men with advanced prostate cancer.The prostate is a walnut-size gland at the base of a man's bladder. Although the gland may enlarge without cancer being present, prostate cancer becomes a significant risk for men over 40, and about one in 11 men will develop the cancer during their lifetime.

Prostate cancer is the third leading cancer killer among males in the United States, the American Cancer Society said Monday. The group estimates about 103,000 new cases of prostate cancer and about 28,500 deaths will be reported in 1989.

Doctors believe the male hormone testosterone stimulates cancer cell growth by the diseased prostate.

Leuprolide sharply reduces production of testosterone by the testes.