The Food and Drug Administration said this week there is no significant risk that a person can contract the AIDS virus from RhoGam or other medicines derived from blood plasma.

The agency, along with the Pentagon, the federal Centers for Disease Control and RhoGam's manufacturer, Ortho Diagnostic Systems, Inc., are investigating allegations that an enlisted Army woman and her infant may have contracted AIDS from the drug used to prevent a rare condition of blood incompatibility in some pregnant women and their unborn children.

An FDA spokesman said that investigators were checking to see if the woman could have contracted the AIDS virus through some other route of transmission.

The virus causing acquired immune deficiency syndrome is usually transmitted in blood or semen through sharing of contaminated intravenous drug needles or during sexual intercourse. It also can be passed from a pregnant mother to her fetus.

The FDA said it believes it is "very highly unlikely" the AIDS virus could have been passed in RhoGam or similar drugs for several reasons.

"In the past 20 years, about 500,000 doses of RhoGam have been given in the United States each year with no documented transmission of any infectious disease," the statement said.

Also, a CDC study of drug products derived from blood plasma last year concluded there was no epidemiological or laboratory evidence that there was any "discernible risk of transmitting AIDS virus infection in these products."

In addition, the FDA spokesman said, since 1985 the manufacturer of RhoGam has required all suppliers of the plasma that is used as a raw material for RhoGam to test for and certify that the plasma is free of AIDS antibodies. The lot of RhoGam under investigation was tested and certified free of AIDS antibodies.

RhoGam is given to pregnant women whose blood type is Rh-negative to prevent a blood incompatibility condition when their infants have Rh-positive blood.