One of this country's most prominent activists for democracy and development in Haiti was fatally injured over the weekend when his car was struck by a stolen vehicle driven by a teenager, D.C. police said.

Marx Aristide, 37, of Silver Spring and a 30-year-old Maryland woman who was described by friends as his fiancee, were hit Saturday evening in Northwest Washington, police said.

Aristide, an economist who had once run the Washington Office on Haiti, a nonprofit human rights group, was described as an eloquent voice for his native island. He died about noon Sunday at Howard University Hospital, police said.

Authorities declined to identify the woman, calling her a witness to the accident, which occurred about 6:25 p.m. Saturday at Florida Avenue and 14th Street.

The 14-year-old driver of the stolen Jeep was charged with second-degree murder, leaving an accident and reckless driving, police said.

News reports of Aristide's writing and speaking, and associates interviewed yesterday, portrayed him as vigorous in urging Haitian Americans to contribute their talents and energies to help relieve Haiti's grinding poverty.

"He started a nonprofit organization called the Skill Share Foundation," said Haitian American leader Mildred Charles. The group reached out to Haitian expatriates to "share their knowledge and expertise in trying to rebuild Haiti," he said.

In addition, after Haitian President Jean Bertrand Aristide was apparently forced from office this year -- an action to which Marx Aristide objected -- he went to Haiti to observe the new interim government and the state of human rights, according to Washington-based rights activist Nicole Lee.

She said that he told audiences that despite his name, he was related to neither President Aristide nor Karl Marx.

Friends said that after president Aristide left office, Marx Aristide "was very active in challenging" what he considered U.S. policies that had driven him out. He and two others were to discuss Haiti yesterday with the editorial board of The Washington Post; the meeting was canceled.

Bill Fletcher Jr. of TransAfrica Forum, who was to head the delegation, said Aristide would have brought "a visceral connection . . . with the people and the situation in Haiti that was unique."

Marx Aristide was born in the Haitian city of Gonaives, studied at the State University of New York at Stony Brook and did graduate work at Howard University.

His mother lives in New York and he had a daughter, friends said.

Police said that Marx Aristide was headed east on Florida Avenue when his Toyota was struck by the Jeep, which was headed south at high speed on 14th Street NW. The Jeep's driver and another 14-year-old in the car ran but were later arrested, police said. They were not identified because of their age.

Marx Aristide's "life was a message to us all, to stand up and fight for what is right," Mildred Charles said.

Staff researcher Bobbye Pratt contributed to this report.