A 21-year-old woman was ordered sent to St. ELizabeths Hospital for observation yesterday after her arrest Thursday in connection with a fire that caused extensive damage to an apartment house at 3145 Mount Pleasant St. NW last month and left about 200 persons homeless.

Judge Bruce S. Mencher ordered Cricelia Belinda Fenty, formerly of the Mount Pleasant Street address, sent to St. Elizabeths during her arraignment in D.C.Superior Court on an arson charge.

According to D.C. police, the fire, which caused an estimated $275,000 damage tothe apartment house, was started in a clothes closet in the apartment then occupied by Fenty.

Police said Fenty was arrested on a fugitive warrant by Montgomery County Sheriff's deputies Tuesday afternoon at her mother's home at 1703 East West Hwy., Silver SPring. She waived extradition to the District, they said.

According to an affidavit, filed at the arraignment, said Fenty went to a friend house and later committed herself voluntarily to St. Elizabeths.

Investigators were told she left the hospital Feb. 2 against her doctor's advice, according to the affidavit.

Court records also showed that Fenty had lived in the four-story Mount Pleasant Street apartment building for about six weeks and was unemployed.

Dr. Lonard C. Maguigad, a St. Elizabeths staff psychiatrist, told the court yesterday that he had examined Fenty and found her to be mentally ill and incompetent to stand trial. He said she told him she heard voices.

Mencher asked the hospital to provide a further report by April 5 on Fenty's condition.