Months after experts discounted the importance of routine mammograms and Pap smears for many women, the American Cancer Society is warning more explicitly than ever that regular testing for prostate cancer is of questionable value too, and can do men more harm than good.

The cancer society has not recommended routine screening for most men since the mid-1990s, and that is not changing. But the organization is urging doctors to talk frankly with their patients about the risks and limitations of the PSA blood test when offering it.

Two big studies last year suggested prostate cancer screening doesn't necessarily save lives, and any benefits can come at a high price. The widely used PSA test often spots cancers too slow-growing to be deadly. It can yield false-positive readings that result in unnecessary biopsies. And it can lead to treatments that can cause impotence and incontinence.

"We had a revolution" when PSA tests became available and prostate cancer screenings kicked into high gear, said Dr. Len Lichtenfeld, the cancer society's deputy chief medical officer. "Now we're having an evolution. We're learning more about what PSA really tells us."

He added: "We don't know that it truly saves lives the way people want it to save lives."

Some doctors and advocates are troubled by the new guidelines.

"Prostate cancer is still something to be respected if not feared, and we still need to be vigilant. I hope primary care docs or insurance companies don't use the 'softening' of the guidelines as an excuse to not do screening at all," said Dr. David Roberts, medical director of an Atlanta clinic that caters to businessmen.

Dr. Stephen Freedland, an associate professor of urology at Duke University Medical Center, warned that the medical establishment seems to be moving backward on cancer screening.

"We have seen dramatic drops in mortality from breast, prostate and cervical at a time when screening has been increasing, and now we are stepping off the pedal. I don't think that is the right answer," he said.

Men will need to weigh their fear of having a potentially aggressive cancer versus treatment that can cause ugly side effects. Another option if cancer is found is watchful waiting - that is, doing nothing - but that can mean high anxiety.

The cancer society's new guidance released Wednesday urges doctors to:

- Discuss the pros and cons of testing with patients, offering written information or videos that discuss the likelihood of false test results and the side effects of treatment.

- Stop routinely giving the rectal exam because it has not clearly shown a benefit, though it can remain an option.

- Use past PSA readings to determine how often follow-up tests are needed and to guide conversations about treatment.

Cancer experts have been having second thoughts in recent years about the value of regular screening to detect certain types of cancer in its early stages. Last year, a government task force said most women don't need mammograms in their 40s, and a doctors group said most women in their 20s don't need annual Pap tests.

The new advice on prostate cancer runs counter to what men have been told on TV and other public service campaigns for several years.

Prostate cancer screening became a medical mantra in the 1990s, thanks to the development of the PSA test. Some celebrities became advocates for regular testing, including former New York Mayor Rudy Giuliani, who credited a PSA test during a routine exam with helping him beat prostate cancer a decade ago. Actor Brad Garrett from "Everybody Loves Raymond" had an on-the-air digital rectal exam for a TV special.

For American men, prostate cancer is the second-deadliest cancer after lung cancer. An estimated 192,000 new cases and 27,000 deaths from it occurred last year in the United States. But it is often a slow-growing cancer, and depending on a man's age, he may be more likely to die of something else.

Another problem with the PSA test is that an elevated or fast-rising PSA reading can indicate the presence of cancer, but can also be caused by something minor, such as an infection or an enlarged prostate. A biopsy is needed to confirm cancer, and that can cause unnecessary pain and fear.