California scientists believe they have developed a vaccine for gonorrhea.

Such a vaccine has eluded researchers up to now because the bacteria that cause the venereal disease are able to confuse the body's immune system. The bacteria continually change the configuration of a key protein, preventing the immune system from recognizing the invasion.

But a team of Stanford University researchers has found a part of the pilin protein that stays the same.

The pilin proteins make up the pili, which the bacteria use to attach to the urinary tract. The vaccine apparently works by stimulating the immune system to attack the pilin protein, thereby deactivating the pili and preventing the bacteria from attaching.

Because gonorrhea does not occur in other animals, the vaccine must be tested on humans.

Gonorrhea affects more than 1 million people a year in the United States. And although it is usually easily cured by antibiotics, some strains are becoming resistant.

In women, the disease can lead to pelvic inflammatory disease, says researcher Dr. Gary Schoolik, and repeated cases can lead to infertility.

"There is an epidemic of infertility caused by gonorrhea in Southeast Asia and Western Africa," he says. "In parts of Africa, one-quarter of the women are infertile by age 25."

The same researchers also are close to developing a vaccine to prevent urinary tract infections from invading the kidneys. Test on rats have been successful; human tests are to begin this year.