Chief Justice Warren E. Burger yesterday temporarily blocked an abortion planned for a severely retarded Silver Spring woman who became pregnant nearly six months ago after being raped while under 24-hour care at two Maryland institutions for the handicapped.

Burger, acting in an emotionally charged case that raises constitutional questions about the rights of the unborn, postponed a decision on the abortion until noon today at the request of Gerard E. Mitchell, a Rockville lawyer who was appointed earlier this month by a Montgomery County judge to represent the fetus.

Mitchell, whose attempts to prevent the abortion have been rebuffed by Maryland courts, asked the Supreme Court to review the case because the woman, who is 19 years old and deaf, mute and blind, is "incapable of exerising a ersonal choice for abortion," he said in a written petition to the high court.

The woman's "unborn baby . . . faces painful and inhuman deprivation of his or her life unless relief is granted by this court," Mitchell said. In addition, he argued, an abortion performed so late in the woman's pregnancy could endanger the life of the mother.

The legal controversy surrounding the young woman began last month when authorities at two institutions for the handicapped discovered the woman was pregnant. The woman's mother was appointed guardian Sept. 24 and asked the court to authorize an abortion. On Oct. 1, Montgomery County Circuit Court Judge William M. Cave appointed Mitchell as the attorney for the fetus. On Oct. 5, Circuit Court Judge Calvin R. Sanders ruled that the mother, as guardian, could approve the woman's abortion.

Mitchell immediately appealed the ruling to Maryland's Court of Special Appeals, but the court dismissed the appeal two days ago. The same day, the state Court of Appeals decided it would not review the case, in effect allowing the abortion to take place.

Roy A. Niedermayer, attorney for the mother of the pregnant woman, said in an interview yesterday that the abortion should be allowed because "the Supreme Court has ruled that a fetus has no constitutional rights, at least prior to the time" it can live on its own.

Niedermayer said he was referring to the court's 1973 decision in Roe v. Wade, the landmark ruling that held that a woman's basic right to privacy applied to her decision on whether to have an abortion. The court said that no state could interfere with a woman's right to choose an abortion in the first three months of pregnancy and in the second trimester a state could regulate abortion only when considering a woman's health.

"The court said the word 'person' as used in the 14th Amendment does not include the unborn," Niedermayer added. He declined further comment.

In his petition, Mitchell said: "The courts of Maryland are so intimidated by what are perceived to be the dictates of Roe v. Wade . . . that vital state interests are being disregarded."

Mitchell said he and the fetus, which is about 24 weeks old, have "standing to contest the deprivation of the right to life."

Burger postponed the abortion indefinitely so he could study the case more fully; he gave Niedermayer until noon today to respond to Mitchell's petition.

Mitchell's request to the Supreme Court came one month after Maryland State Police confirmed they were investigating the rape of the woman, who at the time was spending five days a week at the Maryland School for the Blind in Baltimore and weekends at the Great Oaks Center in Silver Spring, a state-licensed facility for the mentally retarded.

State police Cpl. Donald R. Chipley said yesterday that investigators are still questioning employes at the two institutions about the woman's rape and have made no arrests in the case. The woman, meanwhile, is now living full time at the Great Oaks Center.

Mitchell also noted in his petition that during a closed court hearing during the first week in October, the pregnant woman's doctor recommended the woman continue her pregnancy to term.