trains of gonorrhea that are resistant to a major class of antibiotics have reached the mainland United States after steady migration from Asia to Hawaii and now to California. Meanwhile in Hawaii, researchers have identified the first cases in the United States of gonorrhea resistant to multiple drugs.

The standard mainland treatment calls for single-dose therapy using one of two classes of antibiotics, fluoroquinolones like ciprofloxacin and ofloxacin and the cephalosporins cefixime and ceftriaxone. But resistance to fluoroquinolones is now found in 60 percent to 80 percent of cases in some East Asian countries and 20 percent of those in Hawaii, where fluoroquinolone use has been largely abandoned.

In the major metropolitan regions of California, fluoroquinolone-resistant gonorrhea has become persistent. Officials at the Centers for Disease Control and Prevention expect to address the problem on Thursday, when they announce new guidelines for treating sexually transmitted diseases.

The new guidelines most likely will change recommendations on fluoroquinolones in treating gonorrhea, said Cynthia Glocker Crick, a spokeswoman. She declined to say whether the changes would be specific to California, but said its health department would issue similar guidelines.

Drug-resistant gonorrhea poses two problems for public health. Incorrect treatment can eliminate symptoms, but not the infection. Patients who think they are cured can pass their resistant bacteria to others. Untreated or undertreated gonorrhea can cause pelvic inflammatory disease and ectopic pregnancies in women and infertility and other problems in both sexes.

Generally, health officials recommend against using a certain antibiotic to treat gonorrhea in local populations where at least 3 percent to 5 percent of the cases show resistance to the drug.

"We began seeing true resistant isolates here in 2001," said Dr. Jeffrey Klausner, deputy health officer of the San Francisco Health Department. "They appeared at a level of 2 to 3 percent a month, and sometimes 5 percent, and have been pretty steady since."

In April 2001, the department advised against fluoroquinolones for gonorrhea.

An epidemiologist at the disease center, Dr. Susan Wang, said similar levels had been reported in Southern California.

"The warning signal from Hawaii told us, It's close to our doorstep, but it's still in the Pacific," Dr. Wang said. "But now it's on the continent and very worrisome. Now, the borders are really down."

In March, Dr. Wang presented data on three cases of gonorrhea in Hawaii with intermediate resistance to one of the cephalosporin drugs and high resistance to fluoroquinolones, the first cases resistant to multiple drugs in the United States.

She presented data on mainland fluoroquinolone-resistant gonorrhea in March at the National S.T.D. Prevention Conference. Its presence showed that the resistant microbe followed the migration of its penicillin-resistant cousin, which first arose in Asia in the 1970's and migrated to Hawaii and California. By 1987, penicillin was abandoned nationally for gonorrhea treatment.

"As goes California, so goes the nation," said Dr. H. Hunter Handsfield, director of S.T.D. control at Public Health-Seattle and King County, where resistant cases were also identified. "It's not a question of if, but when."

The potential loss of half the nation's first-line anti-gonorrheal arsenal has health officials concerned. Dr. Jonathan Zenilman, associate professor of infectious diseases at the Johns Hopkins School of Medicine, said widespread fluoroquinolone resistance would not become a major problem for five or six years.

"So then we look at what is the next option," Dr. Zenilman said. `'It's cephalosporins. These would then become our only first-line therapy."

Relying on cephalosporins and, perhaps, second-tier antibiotics would pose other challenges. Cefixime can cause allergic reactions, and it costs slightly more than fluoroquinolones. Ceftriaxone requires an injection, increasing costs and risks.

"If we eliminate quinolones and are left only with cephalosporins," Dr. Zenilman said, "that's putting a lot of antibiotic pressure on that organism, and eventually it's going to become resistant."