The disparities were particularly acute in 1996, when the study began, and have improved somewhat over two years.
But the gap persisted for many groups, including women, who are most likely to get HIV through sex with a drug user and are also less likely to be in treatment.
The new research comes from the HIV Cost and Utilization Study, the first national data on care for people with HIV and AIDS. Researchers identified about 231,400 American adults with HIV who were receiving at least some medical care outside the military or prison, in all states except Alaska and Hawaii.
From this group, a random sample of more than 2,000 patients was chosen for interviews beginning in early 1996 and again in early 1998. Researchers measured six components of care -- three relating to use of medication and three related to use of doctors and hospitals.
Future research will focus on the cause of the disparities: Are certain patients failing to seek care? Or are the attitudes and practices of doctors and hospitals making it harder for these patients to get it?
"At least on an unconscious level, some providers may have more aggressively tried to provide these treatments to certain patients," said Dr. Martin F. Shapiro of the University of California at Los Angeles, lead author of the study being published Wednesday in the Journal of the American Medical Association.
Shapiro also noted that the differences in care based on insurance type and race persisted, even when researchers took into account such factors as how the person contracted the virus.
This, he and others said, reflects larger disparities in the health system that go well beyond AIDS.
Overall, care improved from 1996 to 1998. At first, just 29 percent of all patients were receiving care that met all six standards. That jumped to 47 percent two years later.
But the care differed widely among groups.
In 1998, for instance, 88 percent of whites were receiving powerful protease inhibitors, but just 80 percent of blacks were.
Similarly, 87 percent of men infected through sex with other men were taking these drugs in 1998, compared with 81 percent of those infected through drug use.
Some of the gap had narrowed, but researchers found that trend had slowed, meaning further improvements were not likely.
While disparities in access to health care are widespread, unlike other diseases, most people with the AIDS virus can trace their infection to one of two sources: homosexual men or intravenous drug users.
Part of the explanation is simple economics. People infected through intravenous drug use, or sex with a drug user, generally have less money, less education and more life problems -- all of which keep them rom getting effective care.
At the same time, the gay community has mobilized around the disease, educating its members about treatment options and the importance of getting care.
But while the AIDS epidemic hit homosexual men first, blacks are the fastest-growing group of victims, now accounting for nearly half of all new infections.
Written By Laura Meckler