The first head-to-head comparison of the nation’s two most popular medicines for prostate trouble found that one gives significant relief while the other is virtually worthless.

The two medicines, Hytrin and Proscar, are taken by millions of older men to relieve the symptoms of an enlarged prostate gland. The study found that Hytrin eases men’s discomfort by about one-third, while Proscar works no better than dummy sugar pills.

For the majority of patients, Proscar is no more than “an expensive placebo,” said Dr. Herbert Lepor of New York University Medical Center, the study’s director. Prostate drugs generally cost $30 to $45 a month.

The study was financed by Merck & Co., which makes Proscar, and Abbott Laboratories Inc., the maker of Hytrin. It was conducted on 1,229 men at Veteran Affairs hospitals.

The results were first reported at a meeting of urologists in May, and preliminary findings from the research were reported a year ago, so the publication of the study had little effect on the pharmaceutical companies’ stock.

On the New York Stock Exchange, Merck was unchanged at $68.75 and Abbott Laboratories fell 50 cents to close at $47 Wednesday.

One-on-one comparisons of popular prescription drugs by their makers are fairly unusual because of the expense and the obvious hazard of losing.

Although both companies approved the study’s design, Merck discounted its significance as publication approached in today’s issue of the New England Journal of Medicine.

Dr. Glenn Gormley, a Merck research official, said that in hindsight, the study was not set up properly to answer the question of which drug is better. He said experts now know Proscar works only in men whose prostate glands are larger than those typical in the study.

About two-thirds of American men suffer enlargement of the walnut-size prostate gland by the time they reach their 60s, and the condition grows more common as men get older. Doctors call it benign prostatic hyperplasia, but it is “benign” only in the sense that it isn’t cancerous.