Researchers have infected mice with the AIDS virus for the first time, moving the lowly rodent to the front lines of the battle against the fatal disease.

Mice have long been a staple of biomedical research, but until scientists in California were able to develop mice with human immune systems - and then get the AIDS virus to spread in them - the animals had been largely useless in AIDS research.The main breakthrough - getting a human immune system to function in mice - has had scientists excited since the work was reported in Science magazine in September.

The current issue of the magazine, out Friday, contains an updated report from the same Stanford University researchers confirming their assumption that they would be able to get the AIDS virus - HIV - to "take" in their special mice.

Mice with standard immune systems are impervious to the AIDS virus.

In another report in Science, scientists at the National Institutes of Health provided additional information on their previously reported success in producing mice that carry the genetic code for the AIDS virus in every cell of their bodies.

A third paper is on the work of scientists at the Hospital for Sick Children in Toronto, Canada, who have transplanted human bone marrow into mice with human-like immune systems. That research is geared toward studying such blood diseases as leukemia and sickle cell anemia.

As previously reported, the human immune system was developed in mice by transplanting liver, thymus, spleen and lymph node cells from aborted human fetuses into them.

The significance of all three reports is not in what has been learned thus far about AIDS or any other specific disease, but rather the demonstrated ability to use mice in new ways.

For example, the Stanford scientists purposely limited the scope of their initial efforts to infect mice with AIDS to observing them for no more than eight weeks, too short to lead to full-blown AIDS, but enough to show researchers the virus would flourish in their new breed of mice.

"By limiting the study to eight weeks, we cannot yet predict whether the mice would get the full AIDS syndrome," said Dr. Irving Weissman, one of the Stanford researchers. "It's too early to tell. This experiment wasn't designed to mimic AIDS in human patients exactly."