Two federal agencies and the pharmaceutical firm that manufactures RhoGam, a blood-derived pregnancy drug, are investigating the drug for its possible connection with the AIDS contamination of a Maryland woman who took it during pregnancy.

However, federal officials stressed yesterday that they have no evidence at this point that the woman was exposed to acquired immune deficiency syndrome through RhoGam.

"Neither public officials nor the firm believe that there was any possibility that AIDS was contracted through the use of the drug," said Christopher Smith, spokesman for the Food and Drug Administration, which is investigating the case along with the Centers for Disease Control in Atlanta.

Johnson & Johnson, whose subsidiary, Ortho Diagnostic Systems Inc., manufactures the drug, has sent letters to physicians saying that the company does not believe AIDS was transmitted by RhoGam to the Maryland woman, who recently tested positive for the AIDS virus, according to a company spokesman.

"This is a singular case of highly speculative origin which is still being investigated," said Robert Kniffin, spokesman for Johnson & Johnson. "RhoGam has been given to an estimated 4.5 to 5 million women in the past 20 years, and there is no case of any disease being transmitted by this product."

The case involves a woman in her mid-twenties who is in the Army and who received RhoGam during a recent pregnancy. After the baby, who is reported to be about 8 months old, was born, the woman and the child were hospitalized at Walter Reed Army Medical Center for AIDS testing. Both tested positive for the AIDS antibodies, according to hospital officials.

Hospital officials refused to discuss specifics of the woman's case, but said that "in the absence of significant risk factors, we asked that this one small batch of RhoGam be looked at to see if it was possibly contaminated."

The case has prompted a Defense Department office to issue a worldwide alert of military facilities, warning them of the possible AIDS contamination of that specific batch of RhoGam -- RHG636. Johnson & Johnson has set up a toll-free hot line, 1-800-526-3875, to answer questions about the drug.

About 350,000 women -- or 15 percent of all pregnant women each year -- take RhoGam to prevent serious blood disease in their infants, Kniffin said. The drug is given if the woman's blood is Rh negative and her baby's blood is Rh positive because the mother's blood may produce antibodies that attack the fetus. RhoGam, an immune globulin blood plasma product that originates with human donors, usually is given at 28 weeks' gestation to pregnant women who are Rh negative, and sometimes repeated at childbirth.

The American College of Obstetricians and Gynecologists said yesterday that there is "little likelihood" that drugs derived from blood plasma products can cause AIDS.

"We have been in touch with the company that manufactures the product, and have been assured that they are testing it as they have since 1985 to make sure that there is no contamination with the AIDs virus," said Laurie Hall, spokeswoman for the medical organization, which represents 26,000 obstetricians and gynecologists.

"We have no reason to change our recommendation that this product should still be used as needed . . . " Hall said.

Dr. John Queenan, chairman of obstetrics and gynecology at Georgetown University School of Medicine, dismissed reports about the federal investigation of RhoGam as "not prudent," and said the drug was "perfectly safe." Queenan said that RhoGam, which is made from plasma of many donors, is manufactured through an alcohol fractionation process. "That would clearly kill the AIDS virus," he said.

Since June 1985, Johnson & Johnson has required all suppliers of RhoGam raw materials to certify that the plasma is free from AIDS antibodies, according to Kniffin. The CDC stated in April 1986 that immune globulin products carry no discernible risk of transmitting AIDS, he said.