For sexually active professional athletes like Magic Johnson, AIDS may be the most dire consequence of a promiscuous lifestyle.

Team physicians say they have been worried for years about the promiscuity of players that puts them at high risk for all sexually transmitted diseases. The doctors say they considered a tragedy such as Johnson's to be inevitable and predict that more cases of HIV will follow.

"I consider the seriousness of sexually transmitted diseases in the same vein as I would consider the seriousness of alcohol abuse or drug abuse or steroids," said Andrew Tucker, a physician for the Cleveland Browns who practices sports medicine at the Cleveland Clinic Foundation.

Many of the doctors interviewed said they regard male professional athletes as a "high risk population" for sexually transmitted diseases because their celebrity and travel create an opportunity to have sexual intercourse with many women, and a sense of invincibility keeps them from heeding warnings about many health issues, including drugs, alcohol and venereal diseases. Although many athletes remain sexually monogamous and conservative, their environment can be conducive to unhealthful behavior.

Still many players are contracting the more common, treatable, sexually transmitted diseases such as gonorrhea, syphilis, chlamydia and genital herpes, according to team physicians.

"The opportunities are unlimited for any kind of sexual relationship and the opportunities are unlimited for illegal substances," said Charles L. Brown, Jr., medical consultant for the New Orleans Saints. "Every year at training camp our players are given a lecture on sexually transmitted diseases, not only AIDS. They are told they must pay attention to the people they go to bed with, they need to know more about their partners if it's possible, and be more circumspect, especially on their travels."

The impact of what the doctors are saying reverberated last week when an AIDS specialist from Montreal revealed that a patient of his said she slept with 50 professional hockey players. She died two years ago.

Joel Greenspan of the National Centers for Disease Control in Atlanta ticked off a list of the top 20 cities in rates for gonorrhea and syphilis, which are epidemic in this country.

"A lot of these cities are on the route of every pro baseball, basketball, hockey and football team," he said. "Anyone going through on a regular basis and not being careful is likely to run into one of these diseases." And, he warned, sports teams must concentrate on prevention, not just treatment, because "HIV may be the next sexually transmitted disease that the athlete acquires."

"Sexually transmitted diseases did not just become an incident issue with Magic Johnson," said Stephen Haas, a physician for the Washington Bullets and president of the NBA Physicians Society. "There were certain concerns before, and it's just become more publicized. It had been a concern along with drugs, along with gambling and the other temptations and vulnerabilities along the way."

None of the doctors interviewed said he had ever kept a player out of a game because of a sexually transmitted disease, although they said that some of these diseases, such as an attack of genital herpes, might be painful enough to prevent an athlete from playing his best. Penicillin and antibacterial drugs can cure or limit the effects on men, but sexually transmitted diseases can have dire health consequences when they appear in women and can be fatal to fetuses or newborns.

Testing and counseling for the diseases vary from team to team and league to league. None of the leagues has mandatory testing for HIV or any other sexually transmitted disease.

Although doctors say they have tried to educate the players about the risks they are taking, they were generally pessimistic that their warnings would have a lasting effect.

The NBA holds a mandatory seminar for rookies each year in Dallas addressing health concerns and other issues. The NBA has gone so far as to hire actresses to portray prostitutes and test whether rookies will give up their room keys or agree to sex. The next day the actresses come to the seminar and put the players on the spot.

One doctor, Arthur Pappas, medical director for the Boston Red Sox and a minority owner in the team, said he has seen a definite decline in such diseases among baseball players in the past two years and hopes that increased knowledge has changed behavior patterns. "I think it's less of a problem now than it was in the past," he said, "knowing the number of people I've treated in the past with discharge or urethritis who I would have referred to a urologist. It was not uncommon with home and visiting teams. It is infrequent at this point."

Jeffrey Minkoff is a team physician for the New Jersey Nets and the New York Islanders and served as president of the NHL physicians association. He considers it a particularly difficult problem to determine the impact of sexually transmitted diseases. "Alcohol and drugs make their use evident in performance ultimately and cannot be hidden," he said. "HIV is not apparent symptomatically for years."

Cleveland's Browns and Cavaliers employ a group of doctors from the Cleveland Clinic Foundation who emphasize preventive medicine and try to keep close surveillance of players' health. "We do see a number of cases of things like gonorrhea and chlamydia among the players routinely," said Tucker. And with syphilis on the rise in the general population, he said, both teams screen for syphilis in players' standard blood workups. Brown, the Saints physician, said a blood test for syphilis is also part of the standard physical for Saints players and prospective draftees in light of a serious resurgence of the disease in Louisiana.

According to the CDC, New Orleans has the third-highest rate of syphilis among major U.S. cities behind Atlanta and Washington. Atlanta's rate is 221.8 cases per 100,000 people, more than 10 times the rate nationally. Gonorrhea is even more rampant nationally. Again Atlanta has the highest rate -- 753.5 cases per 100,000.

In interviews with doctors the term "high risk population" was used repeatedly to refer to professional athletes. By most accounts, until fairly recently many players had numerous, casual sexual encounters in different cities over the course of a year, did not protect themselves with condoms and gave little thought to sexually transmitted diseases. Instances of players sharing a single female partner, such as the case the Montreal doctor documented, also were known.

"They have an immortality view that 'it's not going to happen to me, it's going to happen to the next person,' " said Brown. But interest in health information has been "significantly heightened by the events of the last" few weeks, he said. "I'm getting questions I've never been asked before. . . . We took the opportunity to review the meaning of the word HIV antibody and the meaning of the word AIDS and how the immune system works, and we had a very attentive audience."