Black Americans are four times as likely as whites to develop kidney failure, but they are much less likely than whites to receive a kidney transplant -- especially the most successful kind: a kidney donated by a living relative, a new report says.

Without a transplant, patients with long-term kidney failure must undergo dialysis several times a week for the rest of their lives. More than 116,000 Americans are currently receiving kidney dialysis, and about 9,000 kidney transplants are performed each year.

The report by the American Society of Transplant Physicians concludes that a combination of social, biological and economic factors accounts for the racial disparity -- particularly a shortage of black organ donors.

The report said other potential reasons include the fact that blacks are less likely than whites to have private health insurance, the fact that kidney transplants have a lower success rate in blacks than in whites, and the possibility that doctors and hospitals may be less likely to offer transplantation as an option to black patients.

Secretary of Health and Human Services Louis W. Sullivan said his department has contracted with the Rand Corp. to study the "unexplained discrepancies" in organ transplantation between blacks and whites. The department also is trying to identify better methods of educating minorities about organ donation and transplants.

"We are encouraged that in some areas of the country donation rates among minority groups are on the rise," he said. In St. Louis in 1990, for example, 16 percent of transplanted kidneys were donated by blacks, compared with 8 percent in 1989.

In 1987, about 24 percent of whites who had recently developed kidney failure received a kidney transplant, compared with 15 percent of blacks, according to government figures quoted in the report published in today's New England Journal of Medicine. The report found that blacks were also much less likely than whites to receive pancreas and liver transplants.

Blacks were only half as likely as whites to receive a kidney from a relative. Twenty-five percent of kidneys received by white patients came from a living relative, compared with about 12 percent of kidneys received by black patients. The rest of the kidneys were obtained after death from people who had agreed to be organ donors.

Kidneys separate water and waste products from the blood and excrete them as urine. Dialysis is a process that, in case of kidney failure, can eliminate impurities from the blood mechanically.

The shortage of black kidney donors has a major impact on the care of blacks with kidney disease because people of the same race are more likely to share similar blood groups and cell-surface proteins, which are used to "match" a donated kidney with a recipient, said Bertram L. Kasiske of the University of Minnesota, the report's principal author.

How long a patient must wait for a transplant depends on whether a reasonably well-matched organ can be found. A close match also makes it less likely that the body will reject the implanted organ. A government report last year found that black patients wait almost twice as long as white patients before receiving a kidney transplant.

Because whites make up the majority of organ donors, Kasiske said, "blacks are more likely to get a kidney that is not as well matched." He added that the society's Patient Care and Education Committee, which prepared the report, "concluded that the first thing that could be done . . . would be to increase the number of blacks in the donor pool, so blacks would have a better chance of getting a kidney from another black."

Kasiske said data from transplant centers, organ donor programs and national surveys suggest that blacks are less likely than whites to agree to donate organs. The reasons are unknown, although educational and cultural differences may play a role. Since the 1970s, a number of studies also have found that the long-term success of kidney transplants is at least 10 percent lower in blacks than in whites.

Kasiske said it is not known whether the fact that blacks are more likely to receive poorly matched organs entirely explains this higher failure rate, or whether other biological factors contribute. "We don't know all the things that lead to good graft survival," he said.

The report suggested that economic and social factors may make doctors and hospitals less likely to offer transplants to black patients. For instance, the federal Medicaid program insures all patients with long-term kidney failure, but does not cover the entire cost of a kidney transplant, so doctors may be more willing to perform transplants on patients with private insurance.

It suggested that doctors also may be reluctant to perform transplants in poor black patients because they suspect them of abusing drugs or because they believe patients will not follow medical instructions.