SAN FRANCISCO, JUNE 19 -- In the first of many protests planned to disrupt the 6th International AIDS Conference, hundreds of activists swept through the city's financial district tonight, chanting slogans attacking U.S. immigration policies that discriminate against people infected with the AIDS virus.

"INS, you can't hide, we charge you with genocide," they shouted. At least nine people were arrested as they tried to enter the area headquarters of the Immigration and Naturalization Service. The march began a week of protest that some say could turn violent, and that all expect to test the city's reputation as a national symbol of urban civility.

"We hope this will be a week without violence," said Kevin Farrell, a spokesman for AIDS Coalition to Unleash Power (ACTUP), the organization of AIDS activists that is scheduled to orchestrate many of the planned protests. "No violence will be started, continued or condoned by any ACTUP organization."

Despite those assurances, tensions are high in the city and San Francisco police were on full alert as thousands of delegates arrived for the AIDS conference. In addition, tens of thousands of gay men and lesbians are expected to protest and celebrate Gay and Lesbian Pride Week.

Although it is long, the meeting's scientific program so far has received second billing. The conference has been the world's most important annual AIDS meeting, but over the past few years, as its political significance has grown, its scientific impact has diminished steadily.

In part, that is because AIDS no longer is a complete medical mystery but a major epidemic that has drawn billions of dollars of federal research funds in the United States alone and the intellectual energy of many of the world's most able scientists. Three or four years ago, it was common for important discoveries to be unveiled at the AIDS meeting.

In an odd way progress has also hurt the conference. To most scientists, AIDS no longer is an "issue" but a disease. To many who will attend, this meeting is just another specialty conference, like those held for every malady from heart disease to arthritis.

In 1985, when the meeting was begun, so little was known about the AIDS virus that each development, every new piece of the puzzle, was considered significant. Now these highly public meetings have become more notable as political and theatrical occasions than as research forums.

"We still need a forum like this to exchange clinical and scientific information on AIDS," said Samuel Broder, director of the National Cancer Institute and a leading AIDS researcher. "I certainly don't see how violence or disruption can help alleviate death and human suffering. And that is why we are all doing this work, isn't it?"

Nearly 2,500 reports will be presented here this week, many by the world's top AIDS specialists. But no matter their quality, the week promises to be consumed with demonstrations. That partly reflects anger of AIDS activists that after a decade, no cure, vaccine or long-term therapies have emerged.

But demonstrations also became inevitable as soon as organizers decided to hold the meeting in the American city most closely identified with gay life and AIDS.

The U.S. immigration policy that bars people with the AIDS virus from entering the country without a special waiver has prompted months of protests. Dozens of scientists, major medical organizations such as the International Red Cross, and several countries have urged their researchers to boycott the meeting. Even the official conference program, supported by the U.S. Public Health Service and the National Institutes of Health among many other organizations, denounces the U.S. policy.

"The conference believes the U.S. policy restricting entry of HIV-infected individuals is discriminatory, unjustified by medical knowledge regarding transmission of HIV, and counterproductive to the goal of identifying solutions to the AIDS pandemic," the program states.

But the issue is one that many activists say privately they are glad to have because it encourages sympathy for AIDS sufferers in a day when exponential increases in money spent on AIDS has led to a decline in popular concern. Many AIDS scientists feel that there is plenty of money for basic research.